CANCER-ASSOCIATED SCM-RECOGNITION FACTOR, PREPARATION AND METHOD OF USE

Abstract: A cancer recognition factor (SCM factor) useful in the performance of the structuredness of the cytoplasmic matrix (SCM) test has been isolated, purified to substantial homogeneity, and characterized, and methods for its use have been described. The factor is a peptide of at least 9 amino acid residues including a core sequence of 9 amino acid residues having an amphipathicity profile substantially equivalent to that of the sequence F-L-M-I-D-Q-N-T-K and produces at least a 10 percent decrease in the intracellular fluorescence polarization value of SCM-responding lymphocytes from donors afflicted with cancer. A synthetic SCM factor representing a consensus sequence of M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K is fully active. Antibodies specific for SCM factor are useful in immunoassays that can detect the factor, including detection in cancer cells grown in vitro. The SCM factor is useful for screening of blood samples and other body fluids or cell aspirates for the presence of malignancy in the donor. The multiple action spectrum of the SCM factor including cancer proliferation and invasion promotion, as well as inhibition of the host's immune defense mechanisms and synthesis of SCM factor by cancer cells, represents a novel target for cancer management. Methods for reducing in vivo activity of the SCM factor, such as dialysis or antibody neutralization, can also be useful in the management of cancer.

Description: CANCER-ASSOCIATED SCM-RECOGNITION FACTOR, PREPARATION AND METHOD OF USE BACKGROUND Many diseases occurring in humans and animals can be detected by the presence of foreign substances, particularly in the blood, the substances being specifically associated with a disease or condition. Tests for antigens or other such substances produced as a result of such diseases show great promise as a diagnostic tool for the early detection of the particular disease which produced the antigen or other substance. Procedures for the detection of such substances must be reliable, reproducible, and sensitive in order to constitute a practical diagnostic procedure for health care providers. In addition, any such procedure should be able to be carried out quickly and inexpensively by persons of ordinary skill and training in laboratory procedures. For example, in the treatment of the various malignancies that afflict humans and animals, referred to generally as cancer, it is recognized that early detection is the key to effective treatment, especially as most therapeutic procedures are more effective and safer in relatively early stages of cancer than in later stages. For example, many chemotherapeutic drugs that are toxic to malignant cells are also toxic to normal cells, and the higher doses required to cure or arrest more advanced cases of cancer can cause uncomfortable and serious side effects. Also, surgery is most often effective only before the disease has spread or metastasized. Far too many cases of cancer are only discovered too late for effective treatment. Accordingly, there has been and continues to be a great need for reliable tests that can diagnose cancer at early stages, and a great deal of research effort has gone to this end. In this connection new tests and procedures are being developed to effect early diagnosis of cancer. One extremely desirable aspect of such a test is its ability either to detect all types of cancer generally, or to detect specific types of cancer, depending on the materials used. The former application of such a test is very important in mass screenings of large patient populations, as would be done in routine checkups. In such mass screenings a test dependent on a particular type of cancer would not be desirable, as there are literally hundreds, if not thousands, of types of cancer and a test that could spot only one or a few types of the disease is far too likely to miss many cases of cancer. In general, these patients would present either no symptoms or vague generalized symptoms that could not be readily linked to a particular type of cancer, so there would be no basis for suspecting a particular type and administering a test specific for that type. In contrast, once the presence of malignancy is known or strongly suspected, it would be desirable to have a test that could pinpoint the particular type of malignancy present. Such a test could add greatly to the efficiency of treatment, because many of the most effective cancer therapies, such as chemotherapeutic agents, are only effective against one type of cancer or at best, a narrow range of types, and the wrong chemotherapy can do more harm than good. In an effort to meet this need and to improve the diagnosis and early detection of cancer in human and animal bodies, a test procedure has been developed which involves the measurement of changes in the structuredness of the cytoplasmic matrix (SCM) of living lymphocytes when exposed either to phytohaemagglutinin or to cancer- associated antigens. This procedure has been described in L. Cercek, B. Cercek, and C.I.V. Franklin, "Biophysical Differentiation Between Lymphocytes from Healthy Donors, Patients with Malignant Diseases and Other Disorders," Brit J. Cancer 29. 345-352 (1974), and L. Cercek and B. Cercek, "Application of the Phenomenon of Changes in the Structuredness of Cytoplasmic Matrix (SCM) in the Diagnosis of Malignant Disorders: a Review," Europ. J. Cancer 13. 903-915 (1977). In accordance with this procedure, a subpopulation of potentially SCM-responding lymphocytes is separated from a blood sample of the patient being tested and the lymphocytes are incubated with malignant tissue or extracts of malignant tissue. If the blood sample donor is afflicted with a malignancy, there is a characteristic SCM response that can be differentiated from the SCM response of lymphocytes from donors not afflicted with a malignancy. The SCM response is determined by measuring changes in intracellular fluorescein fluorescence polarization of the SCM- responding lymphocytes. The changes seen in the SCM test are believed to reflect changes in the internal structure of the lymphocyte as the lymphocyte is activated for synthesis. These changes are seen as a decrease in the fluorescence polarization of the cells when polarized light is used to excite the fluorescein present in the cells. Fluorescence polarization is a measure of intracellular rigidity; the greater the intracellular mobility, the less the measured fluorescence polarization. An observed decrease in fluorescence polarization is thought to result mainly from changes in the conformation of the mitochondria, the energy-producing organelles of the cell. The change in the mitochondria is believed to result from the contractions of the cristae or inner folds of the mitochondrial membrane. The SCM reflects the forces of interaction between macromolecules and small molecules such aε water molecules, ions, adenosine triphosphate, and cyclic adenosine phosphate. Perturbations of these interactions result in changes in the SCM. The SCM test is capable of responding to a relatively small quantity of malignant cells. About 10 9 cells in a person weighing 70 kg are enough to cause the lymphocytes to respond in the SCM test in the characteristic pattern of malignancy. In mice, when as few as 3.5 X 10 5 Ehrlich ascites (tumor) cells are implanted, the pattern of the response in the SCM test iε altered; response to cancer-specific antigens is induced, while the normal response to phytohaemagglutinin is virtually eliminated (L. Cercek and B. Cercek, "Changes in SCM-Responses of Lymphocytes in Mice After Implantation with Ehrlich Ascites Cells," Europ. J. Cancer 17. 167-171 (1981)). The SCM test allows early detection of cancer, often much earlier than is possible by conventional methods, with relatively little discomfort to the patient except as may be involved in taking a blood sample. However, this procedure does have disadvantages. For example, it requires preparation of crude extracts from tumor tissues and the like or the use of the tumor tissue itself as a source of cancer- associated antigens. There are several major problems with the use of malignant tissue or extracts of such tissue in the SCM test. For example, it is sometimes difficult to obtain the required quantity of tissue. Also, the use of whole tissues or crude extracts of tissues can introduce interfering substances into the test procedure. These interfering substances can adversely affect the sensitivity of the test or adversely affect the test results themselves. The presence or absence of these interfering substances can easily vary from batch to batch of malignant tissue, introducing undesirable variability into the SCM test. Additionally, because the interfering substances are present in whole tissue or crude extracts, they are very difficult to identify or quantitate. Accordingly it is very desirable to identify, separate, and purify the factor or factors that provoke a response by SCM-responding lymphocytes. The use of such purified factor or factors would enhance the SCM cancer screening test because interfering substances would not be present, and would aid in the study of cancer, its causes and its effects on human and animal bodies. The availability of purified factors would allow the production of specific antibodies against them. Such antibodies would be useful for both diagnosis and treatment of cancer. It is also very desirable to determine the complete chemical composition and structure of such SCM- active factors. If they turn out to be peptides or proteins, it would be especially desirable to determine their complete amino acid sequence. The knowledge of their complete amino acid sequence would allow their production by either solid-phase peptide synthesis techniques or recombinant DNA techniques. The application of these techniques would result in the availability of larger quantities of the factors without the necessity of isolating them from blood plasma or cancer tissue. SUMMARY We have discovered cancer recognition factors in body fluids, in particular in blood plasma, and purified these factors to substantial homogeneity. These factors produce a response in SCM-responding lymphocytes obtained from a donor with cancer that is identical to the response produced in such lymphocytes by cancer- associated extracts and/or tumor tissue in the SCM test. As described herein, the factors are designated in the singular and are referred to herein as the "cancer recognition factor useful in the structuredness of the cytoplasmic matrix (SCM) test," as the "cancer recognition factor," or merely as the "SCM factor." The activity of the SCM factor can be demonstrated at a number of stages of purification of the factor from plasma, beginning with a step of ultrafiltration. In this step molecules with an apparent molecular weight of leεs than 1,000 daltons are separated from molecules with a larger molecular weight by ultra filtration through a filter with a nominal molecular weight cutoff of 1,000 daltons. The SCM factor is found in the fraction pasεing through the filter, in contrast to most other peptides and all proteins. The factor consists essentially of low molecular weight peptide passing through such filters and producing at least a ten percent decrease in the intracellular fluorescence polarization value of SCM-responding lymphocytes isolated from donors afflicted with cancer when used to challenge lymphocytes in the standard SCM test. Further purification of the SCM factor, aε described below, results in a substantially homogeneous peptide of 29 to 35 amino acid residueε. Becauεe the SCM factorε isolated from blood plasma sampleε obtained from patients with different types of cancer were largely homologous, a synthetic 29-amino-acid peptide, designated "synthetic SCM factor," was prepared. This peptide was fully active in the SCM test; certain fragments of this peptide, as described below, were also active in the SCM test. 1. Peptides Possessing SCM-Factor Activity As determined from studies on fragments of synthetic SCM factor, a peptide of at least 9 amino acid residueε including a core εequence of 9 amino acid reεidueε having an amphipathicity profile substantially equivalent to that of the sequence F-L-M-I-D-Q-N-T-K is expected to have SCM-factor activity and to produce at least a 10 percent decrease in the intracellular fluorescence polarization value of SCM-responding lymphocytes from donors afflicted with cancer. The core sequence of 9 amino acid residues can be F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K. In this sequence, X 15 and X 17 are each independently selected from the group consisting of I, L, and V; X 18 is selected from the group consisting of D and E; X 19 and X 20 are each independently selected from the group consiεting of Q and N; and X 21 is selected from the group consisting of S and T. These substitutionε are exampleε of "conεervative" amino acidε εubεtitutionε, in which substitution of one of the amino acids of the group for another amino acid is expected to cause essentially no change in the structure of activity of the peptide because the properties of the amino acids are so similar. In particular, the core sequence can be F-L-M-I-D-Q-N-T-K. Determination of the amino acid sequenceε of purified SCM factor obtained from blood plaεma with patients with different types of cancer has led to the conclusion that such factors consist essentially of a peptide of from 29 to 35 amino acid residues including a core sequence at amino acid residues 14-22 of F-L-M-I-X 18 - Q-N-T-K, where X 18 is D or E. Particular examples of peptides conforming to this general εequence pattern and having SCM-factor activity include: (1) X.,-I-P-P-X 5 -V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N- T-K-X^-P-L-F-M-G-K, where: X, can be V, M, or S; X 5 can be E or D, and X^ can be T or V; particular peptideε of thiε sequence pattern are V-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D- Q-N-T-K-V-P-L-F-M-G-K and M-I-P-P-E-V-K-F-N-K-P-F-V-F-L- M-I-D-Q-N-T-K-V-P-L-F-M-G-K; (2) M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T- K-C-P-C-F-M-G-C; (3) X^I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T- K-C-C-L-F-M-G-K, where X, can be M or V, typically M; (4) X,-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T- K-R-P-L-F-M-G-K, where X, can be R or S, typically S; (5) V-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T- K-C-P-L-F-M-G-K; (6) V-I-P-P-E-V-K-F-N-C-P-F-V-F-L-M-I-D-Q-N-T- K-V-P-L-F-M-G-K; (7) X. j -1-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T- K-C-P-C-F-M-G-C or X^I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q- N-T-K-C-P-C-F-M-G-c-v-v-N-C-T-E, where X., is R or S, where the sequence typically has 29 amino acidε and X 1 is typically R; (8) X^I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-E-Q-N-T- K-S-P-L-F-M-G-K or X-,-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-E-Q- N-T-K-S-P-L-F-M-G-K-V-V-N-P-T-Q, where X, iε V or S, where the sequence typically has 29 amino acidε and X, iε typically V; and (9) X. j -1-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-E-Q-N-T- K-S-P-L-F-M-G-K-V-V-N-P-T-Q, where X, is S or V, typically S. These sequences have considerable homology. Therefore, a "consensus" sequence of 29 amino acidε, M-I- P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K, haε been synthesized. This "consensus" sequence iε identical with one of the sequences determined from sequence analysis of preparations of SCM factorε purified from blood plaεma of a cancer patient, specifically, from patients with colon and lung cancer. Because subεtitution of certain amino acids for other amino acids in thiε εequence, as discussed above, iε not expected to substantially alter the activity of the SCM factor, the following εequence derived from the "consensus" sequence by conservative amino acid subεtitutionε iε alεo expected to have SCM-factor activity: M-X 2 -P-P-X 5 -X 6 -K-F-X 9 -K-P-F- X 13 -F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K-X 23 -P-X 25 -F-M-G-K, in which X 2 , X 6 , X 13 , X 15 , X 17 , ^, and X 25 are each independently selected from the group consisting of I, L, and V; X 5 and X 18 are each independently selected from the group consisting of D and E; X p , X 19 and X 20 are each independently selected from the group consiεting of Q and N; and X 21 iε εelected from the group conεiεting of S and T. Additionally, particular fragmentε of the consensus sequence or of peptides derived from the consenεus sequence by conservative amino acid subεtitution are known (in the caεe of fragments of the consensus sequence itself) or expected (in the case of fragments of peptides derived from the consensus sequence by conservative amino acid εubεtitution) to have SCM- factor activity. The sequences that represent fragments of the consensus sequence are, respectively: F-L-M-I-D- Q-N-T-K (amino acid reεidues 14-22) ; F-N-K-P-F-V-F-L-M-I- D-Q-N-T-K (amino acid residues 8-22) ; F-N-K-P-F-V-F-L-M- I-D-Q-N-T-K-V-P-L-F-M-G-K (amino acid residues 8-29) ; and M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K (amino acid residues 1-22) . The shortest of these peptides, F-L-M-I- D-Q-N-T-K, represents the core sequence itself. The following peptides, derived from these peptides by conservative amino acid substitution, are also expected to have SCM-factor activity: (1) F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K, wherein X 15 and X 17 are each independently selected from the group consisting of I, L, and V; X 18 is εelected from the group conεiεting of D and E; X 19 and X 20 are each independently εelected from the group conεiεting of Q and N; and X 21 iε εelected from the group conεiεting of S and T; (2) F-X 9 -K-P-F-X 13 -F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K, wherein X 13 , X 15 and X 17 are each independently εelected from the group conεiεting of I, L, and V; X 18 iε selected from the group consisting of D and E; X 9 , X 19 and X 20 are each independently εelected from the group conεiεting of Q and N; and X 21 iε selected from the group consisting of S and T; (3) F-X 9 -K-P-F-X 13 -F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K-X 23 - P-X 25 -F-M-G-K, wherein X 13 , X 15 , X 17 , X^, and X 25 are each independently selected from the group consisting of I, L, and V; X 18 iε εelected from the group conεiεting of D and E; X y , X 19 and X 20 are each independently selected from the group consiεting of Q and N; and X 21 is selected from the group consisting of S and T; and (4) M-X 2 -P-P-X 5 -X 6 -K-F-X 9 -K-P-F-X 13 -F-X l5 -M-X 17 - X 18 -X 19 -X 20 -X 21 -K, wherein X 2 , X 6 , X 13 , X 15 and X 17 are each independently selected from the group consisting of I, L, and V; X 5 and X 18 are each independently selected from the group consiεting of D and E; X g , X 19 and X 20 are each independently εelected from the group consisting of Q and N; and X 21 is selected from the group consisting of S and T. 2. Purification of Peptides Possessing SCM-Factor Activity The SCM factor can be purified by ultrafiltering a body fluid from a donor afflicted with cancer in order to separate a first fraction of the body fluid comprising molecules having an apparent molecular weight greater than 1,000 daltonε from a second fraction comprising molecules having an apparent molecular weight of less than 1,000 daltons. The body fluid is selected from the group consiεting of peripheral blood, urine, and plasma. Preferably, after ultrafiltration the factor undergoes a further purification process comprising several stageε, each εtage reεulting in a more highly purified factor. The first stage of this purification process comprises elution from a gel filtration column with a fractionation range of from 0 to about 700 daltons and capable of separating the εaltε from .the ultrafiltrate, _ _ the factor eluting at between about 0.3 and about 0.5 timeε the total chromatographic bed volume. The εecond εtage comprises elution from a gel filtration column having a fractionation range of from about 1500 daltons to about 30,000 daltons, the factor eluting from such a column at between about 0.4 and about 0.6 times the total chromatographic bed volume. The next stage of this purification procesε compriεes elution from an anion-exchange column of diethylaminoethyl cellulose at between about 0.28 M to about 0.31 M of ammonium bicarbonate. The final εtage comprises purifying the factor to substantial homogeneity by reverse-phase high-pressure liquid chromatography. Although it is preferred to use the more highly purified preparations of the factor in the SCM teεt, the factor from any stage of the purification, including the initial ultrafiltrate, can be used in the test. 3. DNA Sequences Coding for the SCM Factor DNA sequences encoding the SCM factor as described above are useful for both diagnostic purposes and for production of large quantities of SCM factor by recombinant DNA procedures. Generally, the desired DNA sequence encodes the SCM factor in isolation from DNA encoding proteins normally accompanying SCM factor. Particularly important are DNA sequences encoding the core sequence of F-L-M-I- D-Q-N-T-K and the consenεuε sequence of M-I-P-P-E-V-K-F- N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K. The DNA sequence can be operably linked to control sequences effective in expreεsing the DNA encoding the SCM factor in compatible host cells. Thiε DNA sequence, incorporating the control sequence, can be included in a vector capable of transfecting at least some of the host cellε within which the DNA can be expressed. Host cells tranεfected with this vector are also within the scope of the invention. 4. Antibodies Specific for the SCM Factor and Their Use Antibodies specific for the substantially purified SCM factors can be prepared by standard methods of preparing antibodies to peptides and are within the scope of the invention. Particularly important are antibodies specific for the core sequence and for the consensus εequence. The antibody can be a monoclonal antibody prepared by methods known in the art. These antibodies can be used in a method for determining the level of SCM factor in a body fluid. The method comprises: (1) mixing the body fluid and the antibody; and (2) determining the extent of reaction between the SCM factor in the body fluid and the antibody by performing an immunoassay. The immunoassay can be a radioimmunoassay, a fluorescence immunoassay, a chemiluminescence immunoassay, an enzyme-linked immunoassay, or an immunoassay dependent on aggregation of antigen-antibody complexes. 5. Use of Labeled SCM Factor to Detect Specific Receptors As an alternative to the SCM test for the detection of cancer, labeled SCM factor can be used to determine the presence of receptors specific for SCM factor on SCM-responding lymphocyteε and the εenεitization of the lymphocytes to the SCM factor. The method for determining the presence of receptors comprises: (1) isolating SCM-responding lymphocytes; (2) waεhing the isolated SCM-responding lymphocytes; (3) incubating the isolated SCM-responding lymphocytes with a saturating quantity of a natural or synthetic SCM factor labeled with a detectable label; and (4) determining the extent of the binding of the labeled SCM factor to the SCM-responding lymphocytes in order to determine the presence of receptors specific for SCM factor on the lymphocytes and the sensitization of the lymphocytes to SCM factor. 6. Use of the SCM Factor in the SCM Test The SCM factor according to the present invention can be used to detect cancer in the SCM test. When using an SCM factor purified from a body fluid of a patient with cancer, it is preferred to use a more highly purified preparation of the factor, particularly a preparation of the factor purified to substantial homogeneity by high-presεure liquid chromatography. However, the factor from any stage of the purification, including the initial ultrafiltrate, can be uεed in the test. The SCM factor produces a positive response in the SCM test in a limited fraction of lymphocytes, known as "SCM-responding lymphocytes," derived from donors having a variety of different types of malignancieε, regardleεε of the type of cancer preεent in the donor from which the SCM factor is isolated; the factor produces essentially no response in the SCM test in lymphocytes derived from donors free of malignancy. This feature makes the SCM factor useful for the general screening of blood samples or other body fluid samples for the presence of malignancy. Most generally, the method for testing lymphocytes from a mammalian donor for the presence or absence of malignancy in the donor comprises: (1) contacting a suspension of the lymphocytes with a subεtantially purified cancer recognition factor (SCM factor) as described above; and (2) determining the decrease in the structuredneεε of the cytoplasmic matrix of the lymphocytes resulting from the εtep of contacting the suspension of the lymphocytes. A preferred method for quantifying the decrease in structuredneεε compriεeε the εtepε of: (1) meaεuring the fluorescence polarization, P s , for an aliquot of the lymphocytes that has been contacted with the cancer recognition factor; (2) measuring the fluorescence polarization, P c , for a control aliquot of the lymphocytes that has not been contacted; and (3) determining the ratio of P s to P c . A ratio of P s to P c lower than about 0.9 indicates a poεitive reεponεe to the SCM factor and the presence of a malignancy in the donor of the lymphocytes. A more preferred method comprises comparing P s to the fluorescence polarization of another aliquot of the lymphocytes contacted with a mitogen, P H , typically phytohaemagglutinin, to determine an SCM response ratio, KR SCH ' where: ^CM = p s/ p κ* An g ^ of lesε than about 0.9 indicates the presence of a malignancy in the donor of the lymphocytes. Alternatively, the method of employing the SCM factor in the SCM test can comprise the stepε of: (1) εeparating potentially SCM-responding lymphocytes from the blood sample; (2) contacting the separated lymphocytes with a cancer recognition factor to εtimulate the lymphocytes; (3) contacting the stimulated lymphocytes with a fluorogenic agent precursor, defined as a nonfluorogenic compound hydrolyzable intracellularly to a fluorogenic agent, to penetrate the lymphocytes for intracellular enzymatic hydrolysis to the fluorogenic agent, thereby generating εtimulated fluorogenic agent- containing lymphocyteε; (4) exciting the stimulated fluorogenic agent-containing lymphocytes with polarized light thereby causing them to fluoresce; (5) meaεuring the vertically and horizontally polarized flύoreεcence emissions from the fluorescing lymphocytes for determining a polarization value for the fluorescing lymphocytes; and (6) comparing the determined polarization value for the stimulated fluor-containing lymphocytes with the polarization value for a control aliquot of lymphocytes from the same donor, thereby to indicate the preεence or abεence of cancer in the body of the donor of the lymphocytes, steps (3) and (4) can occur simultaneouεly. The lymphocytes can be excited with vertically polarized light. The polarization values when vertically polarized light iε used are determined in a fluorescence spectrophotometer in accordance with the relationship: I v " GI U P = I v + GI H where, I v and I H are the polarized fluorescence intensities in the vertical and horizontal planes, respectively; and G is a correction factor for the unequal transmiεεion of the horizontal and vertical componentε of the polarized light through the optical εyεtem of the spectrophotometer. 7. Use of the SCM Factor in the Treatment of Cancer Not only does the present invention provide a diagnostic technique for identifying subjectε afflicted with cancer, it also comprehends methods for the treatment of such subjects. These methodε are baεed on εeveral observations described in detail below. These observations reveal that the SCM factor is produced by cancer cells, and that it has εeveral effectε: enhancement of DNA εynthesis, protection of cancer- associated proteases against inhibition by their natural inhibitor α-l-PI and suppreεεion of the natural cytotoxicity of killer lymphocytes against malignant cells. Such suppression of the natural cytotoxicity of killer lymphocytes can be the result of SCM factor action at various steps of the immune defense mechanism. Such SCM factor action can include decreasing the ability of the effector killer lymphocytes to form a complex with the target cancer cells or blocking of the signal transducing mitogen receptorε in ly phocyteε, thuε decreasing production of cytolysins such as tumor necrosiε factor (TNF) and other cytotoxic and/or cytolytic moleculeε. SCM factor action can also include direct interaction with and inactivation of such cytolytic molecules, and the εcavenging of peroxideε and other oxygen-containing reactive species produced by various leukocytes against cancer cells. Because the SCM factor appears to protect cancer cells in several ways, reduction of the in vivo activity of the SCM factor should increase the efficiency of immunological surveillance by lymphocytes against malignant cells. Most generally, this treatment method is a method of treating a cancer patient where at least one of the body fluids of the patient contains a cancer recognition factor. The factor is a peptide of at least 9 amino acid residues including a core sequence of 9 amino acid residueε having an amphipathicity profile substantially equivalent to that of the sequence F-L-M-I- D-Q-N-T-K. The method compriseε: (1) treating a body fluid containing the cancer recognition factor to reduce the in vivo effect of the factor by εelectively inactivating it; and (2) returning the body fluid to the patient, thereby to enhance the resistance of the patient to the cancer. The body fluid can be peripheral blood. In this case, the step of treating the body fluid can comprise dialysis of the peripheral blood to remove peptides with an apparent molecular weight of less than 1,000 daltons. This selectively inactivates the cancer recognition factor by itε removal from the blood. Alternatively, the εtep of treating the body fluid can comprise neutralizing the cancer recognition factor in the body fluid with an antibody specific for it, or with univalent antigen-binding fragmentε of the antibody, such as Fab fragments or Fab' fragments. As another alternative, the εtep of treating the body fluid can comprise inactivating the cancer recognition factor with an antisenεe peptide whoεe amino acid εequence iε that encoded by the antiεenεe strand of a DNA sequence whose sense strand encodes an SCM factor. These methods can further comprise the step of treating the body fluid with a natural or synthetic protease inhibitor non-homologous with α-l-PI protease inhibitor and non-homologous with any other protease inhibitor that is substantially inhibited by SCM factor, the protease inhibitor used for treatment being capable of inhibiting cancer-asεociated proteaεeε protected against α-l-PI inhibition by SCM factor. They can also further compriεe the step of treating the patient with a clinically acceptable metabolic inhibitor, such as ascorbic acid, that causes a decrease in production of the SCM factor by tumor cells. Because the SCM factor is produced by cancer cells and is found in them, an alternative method of treatment involves directing an anti-cancer substance to cancer cells. This can comprise: (1) tagging an antibody specific for SCM factor with the anti-cancer subεtance; and (2) administering the tagged antibody to a cancer patient so that the tagged antibody can bind to cancer cells of the patient, thereby directing the anti- cancer substance to the cancer cells. The antibody can be a monoclonal antibody. Another alternative method of treatment focuses on the reversal of the NK-suppresεive effect cauεed by SCM factor. As detailed below, this NK-suppressive effect can be localized to a particular region of the SCM factor—the carboxyl-terminal 22 residues. Accordingly, a method of reversing the NK-suppressive action of SCM factor in vivo can comprise administering to a patient at least one of whose body fluids contains SCM factor a SCM- factor-inhibiting subεtance in a quantity εufficient to substantially reverse the NK-suppressive action of the SCM factor and substantially restore normal NK activity of lymphocytes of the patient as measured by in vitro lysis of K562 cells by the lymphocytes. The SCM-factor- inhibiting substance can be antibodies to SCM factor, univalent antigen-binding fragments of antibodies to SCM factor, or antisenεe peptides whoεe amino acid εequenceε are thoεe encoded by the antisense strand of DNA sequences whose sense strand encodes a NK-suppreεεive εequence aε deεcribed below under "Uεe of the SCM Factor in Suppreεεing Natural Killer Activity." 8. Use of the SCM Factor in Imaging Cancer Cellε Becauεe SCM factor is found in cancer cells, antibodies to SCM factor can alεo be uεed to image cancer cells, particularly for diagnostic purposes. The method comprises: (1) labeling the antibody with an imaging substance; and (2) utilizing the labeled antibody to image cancer cells by exposing the cancer cells to the labeled antibody. 9. Use of the SCM Factor in Suppressing Natural Killer Activity Both the substantially purified SCM factor and the synthetic SCM factor suppreεs the natural killer (NK) activity of lymphocytes. This NK-suppressive activity was found to be localized in amino acid residues 8-29 of the synthetic SCM factor, with an amino acid sequence of F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K. Therefore, in accordance with the conservative amino acid subεtitutionε described above, a subεtantially purified peptide of at least 22 amino acid residues including an natural killer-suppressive (NK-suppressive) sequence of F-X 9 -K-P-F-X 13 -F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K-X 23 -P-X 25 -F-M-G-K, wherein X 13 , X 15 , X 17 , X^, and X 25 are each independently selected from the group consisting of I, L, and V; X 1g is selected from the group conεisting of D and E; X 9 , X 19 and X 20 are each independently selected from the group consisting of Q and N; and X 21 is selected from the group consisting of S and T is expected to have NK-suppreεsive activity. Other fragments of the synthetic SCM factor, including fragment Fl (residues 1-22) , F3 (residues 8- 22), F4 (residues 14-22), F5 (residueε 1-13), F7 (residues 14-29) , and F8 (residues 23-29) had no NK- suppressive activity. The ability of SCM factor or portions of SCM factor to exert NK-suppreεεive activity makeε poεsible a method for assessing the effectiveness of an anti-cancer agent capable of inhibiting the growth of malignant cells on a cell culture. In this method, the cell culture includes both lymphocytes exhibiting NK activity and malignant cells. The method comprises: (1) incubating the cell culture with the substantially purified NK-suppressive peptide in a quantity sufficient to substantially suppresε the NK activity of the lymphocyteε of the cell culture; (2) adding the anti-cancer agent to the cell culture in a quantity sufficient to inhibit the growth of the malignant cells; and (3) determining the effect of the anti-cancer agent on the malignant cells by observing the inhibition of growth of the malignant cells caused by the anti- cancer agent in the essential absence of NK activity caused by the lymphocytes. The NK-εuppreεsive peptide or the entire SCM factor molecule can be used to modulate the activity of the immune system. Such modulation can be desirable in preventing rejection of transplants. The substantially purified NK-suppressive peptide can be used to εuppreεε the NK activity of lymphocytes by administering it to the lymphocytes in a quantity sufficient to subεtantially suppress the NK activity of the lymphocytes as measured by the in vitro lysiε of K562 cells. Similarly, a method for inducing immunosuppresεion in vivo can compriεe administering an immunosuppresεive fraction alone or in combination with a pharmaceutically acceptable carrier in a quantity sufficient to create a degree of immunosuppresεion capable of enhancing allograft εurvival. The immunoεuppreεεive fraction can be a εubεtantially purified natural or synthetic SCM factor or a NK-suppresεive peptide. DRAWINGS Theεe and other features, aspectε, and advantageε of the preεent invention will become better underεtood with reference to the following deεcription, appended claimε, and the accompanying drawingε where: Figure l shows the amphipathicity profile of the SCM-active F4 fragment of the synthetic SCM factor, representing amino acid residueε 14-22 of the εynthetic SCM factor; Figure 2 εhows the amphipathicity profile of the SCM-active octapeptide whose sequence iε F-W-G-A-E-G- O-R and which has been previously found to occur as an impurity in some preparations of experimental allergic encephalitogenic peptide (EAE peptide) ; Figure 3 is a schematic depiction of one form of ELISA assay for the SCM factor; Figure 4 showε the results obtained from an experiment in which the reactivity of antiserum raiεed against unconjugated SCM factor, as determined by absorbance at 405 nm in a version of the ELISA assay, was measured as a function of the dilution of the antiserum; and Figure 5 shows the resultε obtained from an experiment in which the reactivity of antiεerum raised against SCM factor conjugated with keyhole limpet hemocyanin (KLH) , as determined by absorbance at 405 nm in a version of the ELISA assay, was measured as a function of the dilution of the antiserum. DEFINITIONS Definitionε for a number of termε which are used in the following Description, Examples, and appended claimε are collected here for convenience. "General": Nonεpecific with reεpect to the particular type of cancer afflicting either the donor of the body fluid from which the SCM factor of the preεent invention iε purified, or the donor of the lymphocytes used with that factor in the SCM test. "Fluorogenic Agent Precursor": A nonfluorogenic compound capable of being taken up by lymphocytes and converted intracellularly by hydrolysis into a fluorogenic compound, of which the example used herein is fluorescein diacetate (FDA) . "Standard SCM Test": An SCM test using 1.0 ml of a lymphocyte suspenεion at 6 X 10° cellε/ml and 0.1 ml of the cancer recognition factor or mitogen, with FDA aε the fluorogenic agent precurεor and uεing an excitation wavelength of 470 nm and an emission wavelength of 510 nm for fluorescence polarization measurements. "Apparent Molecular Weight" and "Nominal Molecular Weight Cutoff": Both of these terms refer to the fact that the separation of molecules by ultrafiltration according to size is approximate for molecules in the size range of SCM factor, and depends on conformation aε well aε εize. Thuε an ultrafilter with a nominal molecular weight cutoff of x daltonε will εeparate moleculeε with an apparent molecular weight of leεε than x daltonε from moleculeε with an apparent molecular weight greater than x daltons. However, some molecules with an actual molecular weight greater than x daltons will pasε through εuch a filter. "Substantially Pure Cancer Recognition Factor": Material exhibiting cancer recognition activity as determined in the SCM test and of such a state of purity that at least about 95% of other molecules with specific biological activity, including all proteins and larger peptides, is not present in the material. The term "substantially purified" refers to the same state of purity. "Trvptic Peptide": A peptide cleaved from a larger peptide by the action of the proteolytic enzyme trypsin, which breaks peptide chains after lysine or arginine residues. DESCRIPTION This invention relates to our discovery and purification to substantial homogeneity of twelve peptides that are general cancer-associated SCM- recognition factors from sera isolated from a number of patients from different types of cancer. These peptides are all between 29 and 35 amino acids in length, cross- react in the SCM teεt, and show a εtriking homology in amino acid sequence. This homology is so striking that a 29-amino acid peptide representing a conεenεuε sequence of the twelve purified peptides has been synthesized. This peptide, designated as "synthetic SCM factor", has the amino acid sequence M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M- I-D-Q-N-T-K-V-P-L-F-M-G-K. This synthetic peptide shareε all of the propertieε of the general cancer-aεεociated SCM-recognition factor iεolated from lymphocyteε, including activity in the SCM test and immunochemical reactivity. Even more unexpectedly, a region of nine amino acids within that sequence, amino acids 14-22, with the sequence F-L-M-I-D-Q-N-T-K, is equally active in the SCM test. Other partial sequences, including amino acids 8-22, 8-29, and 1-22, that incorporate the 14-22 sequence are also fully active. Biological propertieε of both the natural purified and the εynthetic SCM factorε are deεcribed. Theεe propertieε are substantially identical, as far as has been determined, for the natural and synthetic SCM factors, and include: (1) the ability of the SCM factor to modify the SCM responεes of lymphocytes from donors free of malignancy; (2) crosε-reactivity of the factor isolated from donors with various types of cancer in the SCM test; (3) its ability to suppreεε the in vitro natural cytotoxicity of killer lymphocyteε toward malignant cells; and (4) the newly discovered property of the SCM factor of protecting proteaseε that are believed to aid in the proliferation and invasion of cancer cells from inhibition by the natural inhibitor of those proteaseε, α.-1-PI. Furthermore, the homology of the SCM factor with α-l-PI has been discovered, along with the fact that α-l-PI can reverse the responses in vitro of SCM-responding lymphocytes of cancer patients to the SCM factor. A method for purification of the SCM factor from blood plasma to subεtantial homogeneity iε deεcribed, aε are methodε of uεing both the εynthetic SCM factor and the-. SCM factor purified from plaεma aε challenging agentε in the SCM test. Lymphocyte receptor assays and various immunochemical assays, including ELISA assays, are alεo deεcribed, as are DNA sequenceε coding for the SCM factorε and vectorε incorporating theεe εequenceε. Finally, methods of using the SCM factors in the management of cancer are described. I. ISOLATED AND PURIFIED GENERAL CANCER-ASSOCIATED SCM- RECOGNITION FACTORS The general cancer-asεociated SCM-recognition factor waε iεolated and purified to homogeneity from blood plasma obtained from patients with twelve different types of cancer. As detailed below, theεe peptideε all are either 29 or 35 amino acidε in length and are substantially homologous in amino acid sequence. A. Purification The purification of the SCM-recognition factor to substantial homogeneity from blood plasma was performed as described in U.S. Patent Application Serial No. 07/167,007 by Drs. Boriε and Lea Cercek, entitled "General Cancer-aεεociated SCM-recognition Factor, Preparation and Method of Use" and incorporated herein by this reference. The purification procesε preferably occurs in five steps: (l) ultra iltration; (2) desalting; (3) gel filtration; (4) anion-exchange chromatography; and (5) reverse-phase high-pressure liquid chromatography (RP-HPLC) . 1. Ultrafiltration The firεt step in purification of the SCM factor is obtaining an ultrafiltrate from a body fluid of a donor afflicted with cancer. The body fluid can be peripheral blood, blood plasma, or urine; if the fluid is peripheral blood, the blood is centrifuged to separate the red blood cells from the plasma. The donor of the body fluid used for isolation of the SCM factor can be either autologous or allogeneic with reεpect to the lymphocytes used for the SCM test. Alternatively, the SCM factor can be purified from cell aspirates or other cellular materials derived from patients with malignancies. The ultrafiltration process separates the first fraction of the body fluid comprising molecules having an apparent molecular weight greater than 1,000 daltons from a second fraction comprising molecules having an apparent molecular weight lesε than 1,000 daltonε. The general cancer-aεεociated SCM factor of the preεent invention iε found in the second fraction of the ultrafiltrate. The terms "apparent molecular weight" and "nominal molecular weight cutoff" are used herein becauεe ultrafiltration iε a εomewhat imprecise method of separating molecules according to molecular weight in this molecular weight range, and the exact molecular weight excluded by a filter with a nominal molecular weight cutoff of 1,000 daltons depends somewhat on the conformation of the molecule. Molecules larger than 1,000 daltons in actual molecular weight can, in fact, pasε through an ultrafilter with a nominal molecular weight cutoff of 1,000 daltonε if, for example, the moleculeε are relatively long and narrow. In fact, the purified general cancer-associated SCM factors of the present invention are either 29 or 35 amino acids long and have molecular weights of approximately 3,200 or 3,900 daltons, respectively. Neverthelesε, all of these peptides pasε through an ultrafilter with a nominal molecular weight cutoff of 1,000 daltons. Preferably, the separation of the second fraction from the first fraction is performed by filtration of the body fluid through an ultrafilter with a nominal 1,000-dalton molecular weight cutoff, such as, but not limited to, an Amicon™ UM2 or YM2 filter (available from Amicon Corporation, Scientific System Division, Danvers, Massachusettε 01923) . The purity of a preparation of εuch a factor, at the ultrafiltrate εtage or later, can be deεcribed by its specific activity. In this context, the term "specific activity" is defined as the reciprocal of the quantity of protein required to cause a particular degree of decrease, such as 20%, in the intracellular fluorescence polarization value when a particular fraction is used to challenge SCM-responding lymphocytes in the SCM test. The goal of purification of the SCM factor is to increase the specific activity of the SCM factor over the specific activity found in the crude ultrafiltrate. The procesε of purification can therefore be followed by determining the εpecific activity of the purified fractionε at each εtage. Since the protein concentration in the exampleε reported herein iε only determined approximately in terms of ultraviolet absorbance, preferably at 220 nm, and the complete dose- reεponεe curve for the factor haε not yet been determined, the characterization of variouε steps of the purification of the SCM factor described herein in terms of specific activity is only approximate. However, it is clear that the protein concentration decreaεeε markedly aε the factor oveε through the variouε purification steps while the activity of the factor is relatively unaffected, thereby resulting in an increase in specific activity of the SCM factor. Nevertheless, even the ultrafiltrate can properly be described as consisting esεentially of substantially purified general cancer- associated SCM-recognition factor, inasmuch as ultrafiltration through a membrane with a nominal molecular weight cutoff of 1,000 daltons removes from a biological fluid the overwhelming majority of molecules with any biological activity, including all proteinε and larger peptideε. 2. Desalting The next step in the purification of the general cancer-associated SCM factor is a deεalting εtep in which the fraction obtained from ultrafiltration iε loaded on a chromatographic column capable of εeparating the salts therefrom. The material loaded onto the column is then eluted from the column with distilled water, and the portion eluting at an elution volume of between about 0.3 and about 0.5 times the total chromatographic bed volume, containing the SCM factor, is collected. Preferably, the column used in this step is a gel- filtration column with a fractionation range of from 0 to about 700 daltons, such as Sephadex™ G-10 (Pharmacia, Uppsala, Sweden) , a dextran gel. A polyacrylamide gel with corresponding separation characteristicε can also be used. 3. Gel Filtration The next step in the purification is another gel filtration step, again separating according to size. The SCM-containing material obtained from the desalting step is loaded onto another gel filtration column with a fractionation range of from about 1,500 to about 30,000 daltons. Preferably, the gel filtration column material is a dextran such as Sephadex™ G-50, but a corresponding polyacrylamide gel can also be used. The material loaded onto the column is then eluted therefrom with a weak aqueous solution of an ammonium salt. Preferably, the ammonium salt is ammonium bicarbonate, more preferably 50 mM ammonium bicarbonate. That portion eluting at an elution volume between about 0.4 times and about 0.6 times the total chromatographic bed volume contains the SCM factor and is collected. 4. Anion-exchange Chromatography The next step in the purification is an anion- exchange chromatography step, separating by charge. The SCM factor-containing material from the previous gel filtration step is loaded onto an anion exchange column, preferably diethylaminoethyl-cellulose (DEAE-cellulose) . The material loaded onto the column is then eluted therefrom with an increasing concentration of an ammonium salt. Preferably, the ammonium salt is ammonium bicarbonate and the increasing concentration of the ammonium salt iε from 10 mM to 1.0 M ammonium bicarbonate. The fraction eluting from the column at about 0.28 M to 0.31 M ammonium bicarbonate contains the SCM factor and is collected. 5. Reverse-phase High-pressure Liquid Chromatography The final step of purification is reverse-phase high-pressure liquid chromatography (RP-HPLC) , which separates by charge and/or hydrophobicity. Typically, the SCM factor-containing material from the DEAE- celluloεe column eluate is loaded onto an Aquapore™ RP- 300 RP-HPLC column with dimensions of 220 mm X 2.1 mm. Elution iε then performed with a combination of two εolventε: initially, 90 volume percent of 0.1 volume percent aqueouε trifluoroacetic acid (TFA) (εolvent A) and 10 volume percent of 0.09 volume percent of TFA in aqueouε 70% acetonitrile (solvent B) , followed by a gradient with an increasing concentration of εolvent B. The SCM factor from all starting materials elutes as an homogeneous peak at a solvent composition of 26 volume percent solvent A and 74 volume percent solvent B. Alternatively, RP-HPLC can be performed on a Beckman Instrumentε Ultrasphere ODS™ column. With this column, elution is then performed with a somewhat different solvent pattern, initially 70 volume percent of solvent A and 30 volume percent of 0.1 volume percent aqueous TFA in aqueous 70% acetonitrile (solvent C) , followed by a gradient with an increasing concentration of solvent C. The SCM factor always elutes aε an homogeneouε peak at a εolvent composition of 43.7 volume percent of solvent A and 56.3 volume percent of solvent C when the Ultrasphere column and this solvent system is used. B. Structure of the Isolated Cancer-associated SCM-recognition Factor The amino acid sequences of the SCM factors isolated from blood plasmas from patients with 12 different types of cancer have been determined by sequential Edman degradation and the resultε reported in Example 14. Certain residues are unidentified; these residues are likely cysteine and are reported herein aε such. In nine out of the twelve cancers, the SCM factor was 29 amino acids long; in the remaining three, an additional six amino acidε were present, yielding a total of 35 amino acids. In seven of twelve of the factor preparations, polymorphismε exist, in that there are conservative substitutionε at one or two poεitions of the peptide. In these cases, the preparation contains two amino acids as identified by Edman degradation at one or two positionε of the peptide. There are never more than two εuch εubstitutions. Alεo, in two caεes, gastric sarcoma and prostate cancer, the SCM factor appears in two forms, one of 29 amino acid residues and the other of 35 amino acid residueε. No formε of intermediate length are found. For εeminoma of the teεteε, only the 35 amino acid form iε found. These slight differences in amino acid sequence do not affect the crosε-reactivity of the factorε in the SCM test. One region of the sequence is nearly invariant — residues 14-22. This sequence is F-L-M-I-D- Q-N-T-K, except in the factors for prostate cancer and seminoma of the teεtes, in which E (glutamate) replaces D (aspartate) at position 18. This change is extremely conservative, inasmuch as glutamate and aspartate have the same charge and differ by only one methyl group. Thiε region iε believed to be extremely significant for the functioning of the SCM factor, as discusεed below. C. Properties of the Isolated, Purified General Cancer-aεεociated SCM-recognition Factor 1. Activity in the SCM Test The purified SCM factors are fully active in the SCM teεt when used as a challenging agent for lymphocytes iεolated from patientε with εeveral different types of malignancies. This activity can be demonstrated by assay at any point during the purification of the factor, starting at the ultrafiltrate. Details of the resultε of εuch aεεayε are given below under "Examples." The greatest activity is obtained with material taken from the final RP-HPLC step. One-tenth milliliter of this fraction, having an approximate protein content of 40 pico oles of peptide, causes a decrease in intracellular fluorescence polarization of as much as 44.6% when used to challenge SCM-responding lymphocytes isolated from cancer patients, but causes no decrease in intracellular fluorescence polarization when used to challenge the same population of lymphocytes isolated from healthy donors. 2. Tryptic Peptides of the Factors Purified preparations of the SCM factor from plasma of patients with lung cancer and breast cancer were subjected to tryptic digestion, followed by purification of the tryptic peptides by RP-HPLC. In each case, a particular fragment eluted at 30.4 volume percent of solvent A and 69.6 volume percent of solvent B, in RP- HPLC using the Aquapore™ RP-300 column. These fractions were found, by sequence analysiε, to be the fragment of the SCM factor conεisting of residueε 8-22. (In both cases, residue 7 is lysine, and trypsin is known to cleave after lysine residues.) These tryptic peptides are fully active in the SCM test (Example 10) . Approximately 5 X 10 "2 femtograms of the tryptic peptide from the SCM factor isolated from plasma from patients with lung cancer (the lung cancer SCM factor), which is approximately 16,000 molecules, gave full activity in the SCM test when used as challenging agent for lymphocytes from donors with cancer. The fragment from the lung cancer SCM factor reacted equally well with lymphocytes from donors with lung cancer and breast cancer, but caused no responεe in the SCM test when used to challenge lymphocytes from normal donors. Further details are given below under "Exampleε." Significantly, both tryptic fragments include the nearly invariant region of the peptide from amino acids 14-22. 3. Cross-reactivity of the SCM Factor The isolated factor of the present invention is designated as a general cancer-asεociated SCM-recognition factor becauεe lymphocyteε iεolated from donorε with all types of cancer respond to all preparations of the factor in the SCM test. The type of cancer afflicting the donor of the lymphocytes need not be the same as the type of cancer afflicting the donor of the body fluid from which the SCM factor was purified (Example 11) . Modification of the SCM Response by the General Cancer-asεociated SCM factor The isolated general cancer-asεociated SCM factor has a property of being able to modify the responεe of potentially SCM-reεponding lymphocyteε obtained from donors free of malignancy when those lymphocytes are contacted with the factor. Before contact, lymphocytes from donors free of malignancy respond only to mitogens, such as phytohaemagglutinin, concanavalin A, and pokeweed mitogen, in the SCM test and do not respond to cancer-associated factors. However, after prolonged contact with the SCM factor, the SCM response of the cells is modified to respond only to cancer-asεociated factorε and not to mitogenε. In other words, contact by such lymphocytes with the SCM factor alterε their response in the SCM test from the normal response of lymphocytes from donors free of malignancy to the response seen with lymphocytes from donors afflicted with cancer. Details on the demonεtration of the modification of the SCM reεponse are given under "Examples." 5. Effect of SCM Factor on Natural Cytotoxicity of Lymphocytes The SCM factor has a property of irreversibly suppreεsing the in vitro spontaneous, natural cytotoxicity not only of the density-εpecific SCM- responding subpopulation of lymphocytes, but also of the general population of peripheral blood lymphocytes isolated by conventional techniques. The suppression of cytotoxicity by εynthetic SCM factor iε dose-dependent; only 11.5 femtomoles of the SCM factor is required for a 50% decrease of the cytotoxic effect. The suppression of cytotoxicity by SCM factor only requires a portion of the synthetic SCM molecule, and the region of the SCM factor responsible for the suppreεεive activity has been determined. It is believed that the SCM factor is involved in the defenεe of cancer cells againεt the attack of killer lymphocyteε. This defense is believed to help the survival and unrestrained growth of cancer cells. The importance of the normal functioning of the immune system in controlling the growth of cancer cells is εeen by the frequent occurrence of unuεual formε of cancer in patientε undergoing immune εuppreεsion. Such immune suppression can occur as a result of a disease such as Acquired Immunodeficiency Syndrome (AIDS) or as a result of the administration of immunosuppreεεive drugs to prevent rejection of transplants. An important example of such an unusual form of cancer is the occurrence of aggresεive forms of Kapoεi'ε Sarcoma, ordinarily a εlowly-εpreading and rarely fatal cancer, in AIDS patients. Details on the decrease of natural toxicity of lymphocyteε are given below under "Exampleε." However, this immunosuppressive effect of the SCM factor could in some instanceε be beneficial to a patient without cancer. For example, in patients receiving tissue transplantε and at riεk of rejection of the tranεplants, suppreεεion of the cytotoxic action of lymphocytes by SCM factor and/or its active portion could help to prevent rejection of the transplants. 6. Homology with α-l-Protease Inhibitor Computer search of the National Biomedical Research Foundation protein sequence data bank unexpectedly revealed that the amino acid sequences of the 12 isolated and purified general cancer-associated SCM-recognition factors are from 82.8% to 89.7% identical to an internal 28-33 amino acid sequence from the glycoprotein cc-1-protease inhibitor (α-l-PI) . The α-l-PI iε a glycoprotein with a molecular weight of 55,000 daltonε; it is a εingle polypeptide chain of 394 reεidueε, and inhibits serine proteases. The sequence of the α-l-PI homologous to the SCM factor is, for factors from 9 out of 12 cancers, between amino acids 358 and 388 with serine at position 359 missing. For the remaining three cancers, gaεtric cancer, adenocarcinoma of the proεtate, and εeminoma of the testes, the homologous sequence is between residues 359 and 393. For the factor from seminoma teεteε, the homology is 100%; for the factor from prostate adenocarcinoma, the homology is 97%; and for the factor from gastric carcinoma, the homology is 94%. (These calculations exclude the unidentified residueε.) In the SCM factorε identified from 9 out of 12 typeε of cancer, the amino-terminal residue is either methionine (5 cancers) , or valine (4 cancers) ; in two additional factorε, it iε arginine. In 11 out of the 12 SCM factorε, the amino acid εerine, originally at poεition 359, next to the methionine and the active εite of α-l-PI at poεition 358, is missing. In the seminoma testes SCM factor, the serine is present at the amino- terminal position, but methionine is absent. The α-l-PI is a glycoprotein normally synthesized in the liver and rapidly released in the blood plasma. Normal levels of this glycoprotein in plasma are reported to be 1.3 g/1. It is an acute- reactive protein and its synthesiε increases up to 4-fold in responεe to inflammatory signalε and other homeostatic needs. It inhibits serine proteases and plays an important role in inflammatory procesεeε by defending tiεsues against attack of proteolytic enzymes released by leukocytes at the site and source of inflammation. It is also thought to be part of the regulatory mechanisms of DNA synthesis, the cell division cycle, and differentiation and maturation procesεes. Inadequate protease inhibition unbalances these processes, often with deleterious consequences to the host. On the other hand, the absence of proteaεe inhibition increases the fertilization efficiency, possibly promoting propagation of individuals with α-l-PI deficiencies. It has been suggested that the level or type of α-l-PI may influence pathophysiological processeε and determine the occurrence, courεe, and εeverity of diεeaεe. However, no genetic variants of α-l-PI are known that could account for the presence of SCM factors in blood plasma, either as a product of an aberrant cleavage at the active center during an inhibition reaction with a protease of a cancer cell, or as a defect in synthesis. There is alεo no evidence that peptideε similar to the SCM factors are generated as a result of breakage caused by ultrafiltration. Plasma from donors free of cancer, including plasma from patients with inflammatory diseases, was subjected to the same ultrafiltration process used as the first stage in the purification procesε of SCM factor. No fragmentε of α-l-PI or peptideε εimilar to the SCM factor were detected in the ultrafiltrates. Furthermore, SCM-responding lymphocytes from cancer patients did not respond in the SCM test to such ultrafiltrates. To eliminate the posεibility that εome specific, aggressive proteases secreted by tumor cells could cleave α-l-PI to produce molecules similar to SCM factors, we incubated overnight at 37°C a variety of human tumor biopsieε and human cultured cancer cell lineε in the preεence of: (a) pure human α-l-PI; (b) a complex of trypεin and o-l-PI; and (c) the molecular weight fraction of cancer patients' plasmas above 5,000 daltons containing α-l-PI, to ascertain that no labile genetic variant of ct-l-PI is present in the plasma of cancer patients. After incubation, tissues or cells were separated by centrifugation and the supernatants were subjected first to ultrafiltration through 1,000-dalton molecular weight cutoff filters (Amicon™ YM2) and then through further chromatographic procedures aε used in the purification of SCM factors. None of these preparations yielded any SCM factor in quantities above thoεe meaεured in εupernatantε of untreated control cancer cellε. 7. Synthesis of SCM Factors by Cancer Cells in Culture Metabolically active human cancer cells grown in culture, including T10806 fibrosarcoma cells, MCF7 breast cancer cells, A2780 ovarian cancer cells, and HCT80 colon cancer cellε, excreted into serum-free tisεue culture media molecules that, when taken through the SCM factor purification process, exhibited optical density peaks with retention times identical to those for SCM factor itself. Sequencing of the picomolar amounts of SCM factor present in the purified preparations of SCM factor from supernatant medium in which the human MCF7 breast cancer cells and HCT80 colon cancer cells were grown confirmed that cells grown in vitro excrete molecules homologous with SCM factor. As shown in Example 24, 15 of the first 16 amino acid residues in the preparation from MCF7 breast cancer cells and 5 of the first 6 amino acid residueε in the preparation from HCT80 colon cancer cells were identical to the sequence obtained from the SCM factor purified from plaεma of breast and colon cancer patients, respectively. These resultε were εupported by ELISA teεts using anti-SCM factor antibody (Example 25) . When ELISA tests were performed on the cultured human cancer cells, the presence of SCM factor was detected in all of the cell lines tested. Different cell lines produced different quantities of SCM factor per cell under identical conditions. This variation might be an expression of differences in carcinogenic potential or metabolic activity of these different cell lines. This is supported by results showing the treatment of MCF7 breast cancer cells and T1080 fibrosarcoma cells with cycloheximide, a translational inhibitor of protein synthesis, caused a decrease in the synthesiε of SCM factor. These resultε are in agreement with our hypothesis that cancer cells actively synthesize SCM factor molecules. To eliminate the possibility that supernatant growth media and/or cultured cells would be contaminated by εome variantε of an α-l-PI produced by fetal cellε, fetal calf εerum was omitted from the growth media used for the last two medium changes. Additionally, we have subjected fetal calf serum to ultrafiltrations through filters with a cutoff of 1,000 daltons and then done the same chromatographic procedure used for the purification of SCM factor. The RP-HPLC eluate resulting did not show an optical density peak at the retention time characteristic of SCM factor molecules. However, another peak adjacent to that for SCM factor was collected in εequence. There was a non-linear sequence homology of 44.7% of the amino acidε present between this peak and SCM factor that could indicate a similar genetic origin, but the difference in sequence is too large to justify any conclusion that SCM factor, like α-fetoproteins, is a product of cancer cell dedifferentiation. This suggeεtε that SCM factor is not an ectopic, dedifferentiation tumor marker. More importantly, the SCM factor itself was not present in the fetal calf serum. Active protein εyntheεiε iε required for production of SCM factor by cancer cellε. Example 26 εhowε that treatment of cultured human cancer cells with the protein synthesis inhibitor cycloheximide considerably decreased the synthesiε of the SCM factor aε determined by the ELISA assay. Similarly, Example 30 shows that addition of ascorbate ions to cultures of MCF7 breast cancer cells considerably decreased the syntheεiε of SCM factor by the ELISA aεεay. Since ascorbate ions can inhibit protein synthesis by reverting mitochondria of cancer cells into the idle, orthodox conformation, as described in L. Cercek & B. Cercek, "Effect of Aεcorbate Ions on Intracellular Fluorescein Emission Polarization Spectra in Cancer and Normal Proliferating Cells," Cancer Detection & Prevention 10, 1-20 (1987) , these resultε confirm that active protein εyntheεiε iε required for production of SCM factor. 8. Stimulation of DNA Synthesis bv SCM Factor As shown in Example 27, SCM factor enhances DNA syntheεiε of rat hepatocytes grown in culture, as determined by tritiated thymidine uptake. The enhancement of DNA syntheεiε iε dependent on the doεe of SCM factor adminiεtered. The relationship between the activity of SCM factor in stimulating DNA synthesis and its posεible role in promoting the growth of cancer cells is discussed below. 9. Blockage of o.-1-PI Activity bv SCM Factor SCM factor has no inhibitory or inactivating activity againεt serine proteases, unlike α-l-PI. However, SCM factor can block the inhibitory or inactivating activity of α-l-PI on proteases when SCM factor molecules are added to the protease before or simultaneously with the α-l-PI. This might result in a posεible increase of protease activity in cancer cells producing SCM factor. The possible consequences of this are discussed below. II. SYNTHETIC CANCER-ASSOCIATED SCM-RECOGNITION FACTOR In view of the high degree of sequence homology between the SCM factorε iεolated from 12 different typeε of cancer, a synthetic SCM factor has now been prepared using standard solid-phase peptide synthesis methods. This synthetic SCM factor has a "consenεuε" εequence of 29 amino acidε and εhareε the propertieε and activity of the isolated purified SCM factors. The preparation of a εynthetic SCM factor is desirable for a number of reasonε: (1) availability and quantity without the necessity of iεolation from cancer tissues; (2) uniformity of structure and activity; and (3) the possibility of varying the sequence in order to determine structure-activity relationships. A. Sequence of the Synthetic SCM Factor Molecule The synthetic SCM factor has the amino acid sequence M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P- L-F-M-G-K. This sequence is not the only sequence with 29 amino acids believed to poεεeεε SCM activity. It iε a well-eεtablished principle of protein and peptide chemistry that certain amino acids substitutions, entitled "conservative" amino acid substitutions, can frequently be made in a protein or a peptide without altering either the confirmation or the function of the protein or peptide. Such changes include substituting any of isoleucine (I) , valine (V) , and leucine (L) for any other of these amino acids; aspartic acid (D) for glutamic acid (E) and vice versa; glutamine (Q) for asparagine (N) and vice versa; and serine (S) for threonine (T) and vice verεa. In view of theεe likely equivalencieε, peptides of the sequence M-X 2 -P-P-X 5 -X 6 -K-F-X 9 -K-P-F-X 13 -F-X 15 -M-X 17 - X^-X^-X^-X^-K-X^-P-X^-F-M-G-L, in which: X 2 , X 6 , X 13 , X 15 , X 17 , X^, and X 25 can each be I, L, or V; X 5 and X 18 can each be D or E; ς ,, X 19 and X 20 can each be Q or N; and X 21 can be S or T, are expected to have SCM factor activity. In this deεignation of the sequence, and corresponding designations elsewhere employing subscripts, the number appearing in the subscript indicates the position of the amino acid specified in a factor of 29 amino acids. For example, "X 2 " refers to the second amino acid from the amino-terminus. The above-mentioned substitutions are not the only amino acid substitutions that can be considered "conservative." Other substitutions can also be considered conservative, depending on the environment of the particular amino acid. For example, glycine (G) and alanine (A) can frequently be interchangeable, as can be alanine and valine (V) . Methionine (M) , which is relatively hydrophobic, can frequently be interchanged with leucine and isoleucine, and sometimes with valine. Lysine (K) and arginine (R) are frequently interchangeable in locations in which the significant feature of the amino acid residue is its charge and the differing pK's of these two amino acid residueε are not εignificant. Still other changeε can be conεidered "conεervative" in particular environmentε. B. Properties of the Synthetic SCM Factor 1. Activity in the SCM Test The synthetic SCM factor molecule is highly active in the SCM test. As shown below in Example 15, as little as 2 femtomoles (2 X 10 "15 moles) of the synthetic SCM factor molecule produced a significant, 20%, decrease in intracellular fluorescence polarization in the SCM test when used to challenge SCM-responding lymphocytes. The synthetic peptide is active in the SCM test when used to challenge SCM-responding lymphocytes from donors with tumors of different histological type and in different organs. The correεponding fraction of SCM-responding lymphocytes from normal, healthy donors does not respond to the SCM factor in quantitieε as large as 960 picomoles (960 X 10 "12 moles) . 2. Induction of SCM-recognition Receptors in Lymphocytes from Healthy Donors The synthetic SCM factor can modify the SCM responεe of lymphocyteε from healthy donorε from the reεponse characteriεtic of such lymphocytes (i.e., a response to PHA and no responεe to a cancer-aεεociated factor) to the response characteristic of lymphocytes from donors with cancer (i.e., no response to PHA and a responεe to a cancer-aεεociated factor) . As detailed in Example 19, SCM-responding lymphocytes from healthy donors did not respond to synthetic SCM factor in the SCM test. However, after incubation for 2.5 hours at 37°C in the presence of 400 picomoles of εynthetic SCM factor per 5 x 10° cellε, followed by three washes with phosphate- buffered saline (PBS) , these cellε εhowed a 37% decreaεe in intracellular fluorescence polarization, indicating the induction of receptors that can respond to the synthetic SCM factor. The induction of these receptors requires protein synthesis. When the incubation is carried out in the presence of the protein synthesis inhibitors cycloheximide or actinomycin D at 10 μg/5 X 10 6 cells, no response to synthetic SCM factor was induced, and the normal responεe to the mitogen PHA waε not aboliεhed. 3. Immunogenic Properties of Synthetic SCM Factor The synthetic SCM factor has a predominantly α- helical secondary structure and is large enough to suggest that it could be presented by the major histocompatibility complex (MHC complex) for induction of the immune response. To test this assumption, the synthetic SCM factor was used to immunize experimental animals, as detailed below in Example 20. Both pure synthetic SCM factor and synthetic SCM factor conjugated to keyhole limpet hemocyanin (KLH) were used for immunization. In the latter case, the synthetic SCM factor was conjugated to the KLH via an added carboxy terminal cysteine residue on the SCM factor using N- εuccinyl bromoacetate aε the cross-linking agent. Other carrierε, εuch as polylysine, can also be used for immunization. The use of such carriers is well- known in the art. 4. Effect of Synthetic SCM Factor and Fragments Thereof on Natural Cytotoxicity of Lymphocytes The synthetic SCM factor was shown to suppress the natural cytotoxic activity of lymphocytes against cancer cells (Example 31) . The synthetic SCM factor decreased the natural killing (NK) efficiency of lymphocytes from normal healthy donorε againεt K562 human myeloma target cells by 97% to 99.9% when a dose of 35 femtomoles of synthetic SCM factor was used per lymphocyte. A dose of 11.5 femtomoles per lymphocyte resulted in a 50% decrease in cytotoxicity (Table 23) . Such quantities of SCM factor are expected to be preεent in the immediate εurrounding of metabolically active cancer cellε, which produce theεe moleculeε. Thiε NK- suppressive effect is irreversible and cannot be removed by a thorough 3-times washing of the treated lymphocytes. To find out to which part of the amino acid sequence of the synthetic SCM-factor molecule this NK- suppressive activity can be ascribed, we have tested various synthetic peptide fragments of the synthetic SCM- factor molecule. As can be seen from Example 31 (Table 26) , the NK-suppressive effect was found only in the entire synthetic SCM factor (29 amino acids) and fragment F2 (amino acids 8-29) . None of the fragments that did not contain the carboxyl-terminal region of the synthetic SCM factor, i.e., fragments Fl, F3, F4, and F5 (Table 26) was active, which might indicate that the seven carboyxl- terminal amino acid residueε are reεponεible for the suppression of NK activity of lymphocytes. However, the peptide fragment consiεting of theεe εeven carboxyl- terminal reεidueε, residues 23-29 (fragment F8) did not suppress NK activity, and neither did peptide fragment F7, consisting of residues 14-29. This shows that the shortest sequence possessing NK-suppressive activity resides within the portion of the SCM factor molecule encompasεing reεidueε 8-29, and only the first seven amino-terminal reεidueε are not important for NK- suppressive activity. This is in contrast to the portion of the synthetic SCM-factor molecule that is responεible for protection againεt inhibition by α-l-PI, which iε the firεt seven amino-terminal residues of the molecule, or the portion of the molecule responsible for SCM activity itself, which occurs within the portion of the molecule between amino acid residue 14 and amino acid residue 22. Thus, the SCM factor exerts multiple functions in promoting the growth and invasion of cancer cells and in suppresεing hoεt defenses. Theεe reεultε indicate that for NK εuppreεεive activity to be expressed, the peptide need not contain the first seven amino-terminal residues of the synthetic SCM factor. Fragment F2 has the amino acid sequence F-N- K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K. As explained above, variants of fragment F2 containing conservative amino acid substitutionε are alεo expected to have NK- εuppreεεive activity. Furthermore, aε can be εeen from the reεultε in Example 31, the NK-suppressive action of synthetic SCM factor not only affects the density-specific, SCM- responding subpopulation of lymphocytes, but a wider population spectrum of lymphocytes as iεolated from peripheral blood by uεing conventional denεity-gradient centrifugation techniqueε employing the Hiεtopaque density medium. This indicateε that the effect of εynthetic SCM factor on εuppreεεion of lymphocyte cytotoxicity haε a broad εpectrum of action. This broad spectrum of action includes various mechanismε by which the SCM factor can inhibit the cytotoxicity of lymphocyteε againεt malignant cellε. For example, we have obεerved that complex formation between the lymphocyteε and K562 myeloma cellε, one of the firεt steps in the killing procesε, iε decreaεed when lymphocytes are treated with the SCM factor. Other effects of the SCM factor could be prevention of synthesis of leukolysinε and/or direct inactivation of various cytolytic molecules, such as tumor necrosis factor (TNF) . The NK-suppressive activity of SCM factor or portions of SCM factor can be used to assess the effectivenesε of an anti-cancer agent capable of inhibiting the growth of malignant cellε in a cell culture that includeε both lymphocyteε exhibiting NK activity and malignant cellε. The effectiveness can be assessed by: (1) incubating the cell culture with a substantially purified NK-suppressive peptide, such as intact SCM factor or one of the peptides expected to have NK-suppreεεive activity deεcribed above, in a quantity εufficient to substantially suppreεs the NK activity of the lymphocytes of the cell culture; (2) adding the anti-cancer agent to the cell culture in a quantity εufficient to measurably inhibit the growth of the malignant cells; and (3) determining the effect of the anti-cancer agent on the malignant cells by observing the inhibition of growth of the malignant cells cauεed by the anti- cancer agent in the eεεential absence of NK activity caused by the lymphocytes. C. Production and Activity of Fragments of Synthetic SCM Factor 1. Sequences and Activity of Fragments In order to determine which portion or portions of the synthetic SCM factor is responsible for its activity in the SCM test, five peptide fragments of the εynthetic SCM factor were synthesized, designated Fl through F5. These represented the following portions of the intact moleculeε: Fl, amino acids 1-22; F2, amino acids 8-29; F3, amino acids 8-22; F4, amino acids 14-22; and F5, amino acids 1-13. These fragments have the following amino acid sequenceε: Fl: M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-D-Q-N-T-K; F2: F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K; F3: F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K; F4: F-L-M-I-D-Q-N-T-K; and F5: M-I-P-P-E-V-K-F-N-K-P-F-V-F. Aε detailed below in Example 17, fragmentε Fl, F2, F3, and F4 are all active in the SCM teεt, while fragment F5 iε inactive. All of the active fragmentε contain the 9-amino-acid εegment of F4, and it iε reaεonable that thiε εegment might represent the active site responsible for SCM activity. Not only are peptides Fl through F4 active in the SCM test, variantε of theεe peptideε with conservative amino acid substitutionε are alεo expected to have SCM activity and fall within the scope of the present invention. These conservative subεtitutions, as outlined above, include any of isoleucine, valine, and leucine for any other of these amino acids; aεpartic acid for glutamic acid and vice verεa; aεparagine for glutamine and vice verεa; and serine for threonine and vice versa. The existence of these conservative substitutions means that the following peptides are expected to have SCM activity: M-X 2 -P-P-X 5 -X 6 -K-F-X 9 -K-P-F-X l3 -F-X 15 -M-X 17 -X 18 -X 19 - X JQ —X 21 —K; F— XQ~ —P—F—X.- J —F— X.m—M— X.γ— ig— io-'X? 0 — 21 "" "" 23 ~" 25 *" F-M-G-K; F-X 9 -K-P-F-X 13 -F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 - ; and F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 - . In these sequences, the subεcriptε deεignating particular amino acid residues have the same meaning as stated above in the discuεsion of conservative amino acid substitutions in the entire 29-amino-acid synthetic SCM factor. 2. Use of the Amphipathicity Profile to Determine SCM Activity An amphipathicity profile is a plot of the relative hydrophilicity or hydrophobicity of segmentε of a peptide or protein. Amino acid residues range from quite hydrophilic (e.g., charged residues or serine) to quite hydrophobic (e.g., phenylalanine) . Typically, the plot is presented as a moving average over a short stretch of amino acids within the protein or peptide. For specificity and recognition purposeε, amphipathicity propertieε of short peptides can be as significant as the amino acid sequence itself. As shown below in Example 18, the amphipathicity profile of the SCM-active F4 peptide fragment is strikingly similar to the amphipathicity profile of the synthetic 8-amino-acid peptide with SCM-factor activity having the sequence of F-W-G-A-E-G-Q-R, even though there is only a limited sequence homology between this peptide and the F4 peptide. By contrast, the experimental allergic encephalitogenic peptide (EAE peptide) has a sequence of F-S-W-G-A-E-G-Q-R. The presence of the relatively hydrophilic serine between the hydrophobic residueε phenylalanine and tryptophane alters the amphipathicity profile considerably. As detailed in our prior U.S. Patent Application Serial No. 07/167,007, the EAE peptide haε no SCM factor activity. Given the importance of the amphipathicity profile of a peptide in determining whether the peptide haε SCM factor activity, a peptide of at least 9 amino acid residues including a core sequence of 9 amino acid residues having an amphipathicity profile substantially equivalent to that of the sequence F-L-M-I-D-Q-N-T-K is expected to have SCM factor activity. III. USE OF THE PURIFIED AND SYNTHETIC SCM FACTORS Both the purified and synthetic SCM factors can be used as challenging agents in the SCM test, can be used to prepare antisera for the detection of the SCM factor, and can be used for the generation of DNA sequenceε that carry equivalent genetic information for uεe in a variety of genetic engineering procedureε. As discussed below, this SCM factor can also be used in the management of cancer. A. Performance of the SCM Test The activity of both the purified SCM factor and the synthetic SCM factor, as well as the fragments of the SCM factor, is confirmed by its effect on viable SCM- responding lymphocyteε in accordance with the prior publication by L. Cercek and B. Cercek, "Application of the Phenomenon of Changes in the Structuredness of Cytoplasmic Matrix (SCM) in the Diagnosiε of Malignant Disorders: A Review," Euro . J. Cancer 13. 903-915 (1977) . The general cancer-associated SCM-recognition factor of the present invention produces a significant decrease in the intracellular fluorescence polarization value of potentially SCM-responding lymphocytes from donorε afflicted with cancer when uεed to challenge such lymphocytes in the SCM teεt as performed as described in that article. The degree of decrease of the intracellular fluorescein fluoreεcence polarization value of εuch challenged lymphocytes is subεtantial — at least 20% even if ultrafiltrate from plasma from donors afflicted with cancer is uεed to challenge εuch lymphocyteε, and as great as 40-55% if purified RP-HPLC fractions or synthetic peptides are used. Two previously established procedures are important for the proper performance of the SCM test as reported herein. These procedures are the isolation of potentially SCM-responding lymphocytes and the technique of measuring the fluorescence polarization values themselves, and their conversion into numbers meaningful for the SCM test. _ _ 1. Isolation of SCM-responding Lymphocytes Several procedures for the isolation of potentially SCM-responding lymphocytes are described in the European Journal of Cancer review article, supra. and also in a prior patent application by B. Cercek and L. Cercek, U.S. Application Serial No. 07/260,928, filed October 21, 1988, and entitled "Provision of Density Specific Blood Cells for the Structuredness of the Cytoplasmic Matrix (SCM) Teεt," incorporated herein by thiε reference. The separation of these lymphocyteε from the general lymphocyte population iε important for the proper performance of the SCM teεt, becauεe only a relatively small portion of lymphocytes, approximately 20-25% of the total lymphocyte population, is capable of responding in the SCM test to cancer-asεociated factors. Therefore, to perform the test on unfractionated lymphocytes resultε in a much smaller observed decreaεe in the intracellular polarization value even when the lymphocytes actually capable of responding in the SCM test fully respond to the challenging agent used. Additionally, there exists another fraction of lymphocytes that responds in the SCM test in a different way. These cells do not respond at all to cancer- associated factors, but respond to PHA when isolated from donors with cancer. As detailed below, some variationε of the SCM test compare the response to PHA to a cancer- associated factor, such as a peptide of the present invention, to determine whether or not the donor of the lymphocytes is afflicted with a malignancy. This second fraction of lymphocytes therefore must be rigorously excluded to avoid distorting the results. Immunologically, the SCM-responding lymphocytes are T-cell mononuclear leukocytes. Although not fully understood, it is believed that SCM-responding lymphocytes are involved in the recognition of antigens that are circulating in the blood stream, expressed on cancer cells, or excreted by cancer cells into interstitial spaces of tumors. This recognition of antigenε triggers the body's immune system. Accordingly, these cells become primed to recognize foreign substanceε, εuch aε antigenε, produced by the diεeaεe or condition affecting the body. SCM-reεponding lymphocyteε can be iεolated by uεing either a εingle-denεity εolution, a εtep gradient, or a continuous preformed gradient. a. Isolation Using Single-density Solution For the isolation of SCM-responding lymphocyteε by the εingle-denεity εolution method, a εample of peripheral blood is drawn from a donor and collected in a heparinized tube. After collection, the peripheral blood is treated with iron powder or carbony1-iron powder and the tubes containing the blood-iron powder mixture are placed on a magnet to effect separation of the phagocytic cells along with the iron powder from a blood sample. A portion of the blood sample depleted of phagocytic cells is then transferred to a Ficoll™-Triosil™ density- gradient εolution and centrifuged to effect εeparation of the SCM-reεponding lymphocyteε baεed on density differences. This method of separation typically useε a density-gradient solution having a density of 1.081 g/cm 3 at 25°C and an osmolality of 0.320 Osm/ kg. Centrifugation is carried out at 550 xg for 20 minuteε at a temperature of 25°C. The SCM-reεponding lymphocyteε are recovered using a Pasteur pipette to remove the cell layer separated above the density-gradient material. Removal of the density-gradient material must be avoided as far as is possible as this material includes various heavier plasma and cell components which interfere with the teεt reεultε. Removal of the lighter plaεma material should also be avoided as much as posεible to eliminate the introduction of any contaminating componentε or SCM- nonreεponding cellε into the test samples. Following separation, the SCM-responding lymphocytes are subjected to several washing εtepε, firεt in 0.9% preεervative-free sodium chloride solution, then in complete Dulbecco's phoεphate-buffered saline (PBS) and held at 37°C for subεequent uεe in the SCM teεt procedure. b. Iεolation Using Step Gradient For the isolation of SCM-responding lymphocytes using a step gradient, use a total blood sample depleted of phagocytic cells as described above, or the total - population of peripheral blood lymphocytes can be uεed. The uεe of the total population of blood lymphocyteε iε preferred, as this avoids the use of possibly toxic iron or carbonyl-iron powder. The isolation of the total population of peripheral blood lymphocytes for an heparinized blood sample is alεo performed uεing denεity-gradient centrifugation. This centrifugation step is performed by layering the heparinized blood on top of a solution of density 1.077 g/cm 3 containing a non-ionic synthetic polymer of sucroεe with a molecular weight of about 400,000 and εodium diatrizoate. Both εolutions are equilibrated to room temperature, and the volume of the density solution is at least as great as the volume of heparinized blood. The layered solutions are then centrifuged, typically at 30 minutes at room temperature at 550 xg, so that the lymphocytes are banded at the interface between the solutionε. The lymphocyteε are then collected from the interface. For the step of separation of the SCM- responding lymphocytes, a step gradient is made by layering a solution of density 1.0590 g/cm 3 and osmolality of 0.320 Osm/kg on top of a solution of density 1.0670 g/cm 3 and the same osmolality. These solutionε are typically prepared from polyvinylpyrrolidone-covered silica media such as Percoll™ (Pharmacia, Uppεala, Sweden) . A volume of a blood sample or peripheral blood lymphocytes equal to about one-half the total volume of the step gradient is layered on top of the step gradient, and the mixture is centrifuged typically at 550 xg for 30 minutes. The SCM-reεponding lymphocyteε collect in a visible band between the first and second density solution and are harvested. c. Isolation Using Continuous Preformed Gradient As an alternative to the εtep gradient, a continuouε preformed gradient can be uεed for the final εeparation of SCM-reεponding lymphocyteε. Thiε gradient εpans a density range of between 1.050 g/cm 3 and 1.070 g/cm 3 . It can be generated by centrifuging a solution of polyvinylpyrrolidone-covered silica at 26,000 xg in a 29° fixed-angle rotor or at 11,400 xg in a 34° fixed-angle rotor. 2. Performance of the SCM Test on Iεolated SCM-responding Lymphocytes a. Measurement of SCM Values The method for measuring the fluorescence polarization values of SCM-responding lymphocytes in the SCM test has been described in the European Journal of Cancer review article, supra. as well as in a prior patent application by B. Cercek & L. Cercek, Serial No. 867,079, filed May 27, 1986, entitled "Method for Measuring Polarized Fluorescence Emissions," incorporated herein by this reference. As described in these references, SCM-reεponding lymphocyteε previouεly εeparated from the teεt subject's peripheral blood are incubated in sterile glasε tubeε at 37°C with a known concentration of either a mitogen εuch as phytohaemagglutinin or a cancer-associated antigen such as the general cancer-asεociated SCM-recognition factor which is the subject of the present invention. Other mitogenε than phytohaemagglutinin (PHA) , εuch aε concanavalin A and pokeweed mitogen, have been used, but PHA is preferred for the SCM test. This incubation is initiated by adding 0.1 ml of the appropriately diluted mitogen or antigen to 1 ml of the cell suspenεion at 6 X 10° cellε/ml. The incubation iε then allowed to proceed for 30-60 min. The incubated lymphocytes are then admixed in suspension with a suitable nonfluorogenic compound hydrolyzable intracellularly to a fluorogenic compound, referred to hereinafter as a fluorogenic agent precursor, such as fluorescein diacetate (FDA) . The fluorescein diacetate is used at a final concentration of 2.5 mM or 0.7 mM in complete PBS at pH 7.4 and osmolality of 0.330 Osm/kg and iε diluted from a concentrated stock solution prepared in acetone or glacial acetic acid, respectively. Aliquots of 0.2 ml of control or εtimulated lymphocyte suspensions are slowly injected with a syringe into a beaker containing 3 ml of the FDA substrate solution. The cells are exposed to the FDA for sufficient time (about 5 minutes) to allow for the penetration of the FDA substrate solution into the lymphocytes. Inside the cells, the nonfluorogenic fluorescein diacetate molecules are converted to fluorescein molecules by enzymatic hydrolysiε. The fluor-containing lymphocyteε are iεotropic in their reεponse to polarized light since the polarization of the emitted fluorescence relative to that of the exciting light does not depend on the orientation of the plane-polarized light used to excite the lymphocytes. However, the conventional fluorescence polarization measuring apparatus used herein for these meaεurementε uses vertically polarized exciting light to excite the lymphocytes, so the measurement process is described in terms of vertically polarized exciting light. When exposed to excitation energy in the form of vertically polarized light, the fluorescein molecules emit fluorescence. The relationship between the vertically polarized and horizontally polarized emissionε is measured. This can be done by measuring the polarized fluorescence intensities in both the vertical and horizontal planes and determining a polarization value (P value) in accordance with the following relationship: * " GI U I v + GI H where I v and I H are polarized fluorescence intenεitieε in the vertical and horizontal planeε, reεpectively, and G is a correction factor for the unequal transmission of the horizontal and vertical components of the polarized light through the optical system of the particular equipment used. The value of G is determined by dividing the intensity of the horizontally polarized light by the intensity of the vertically polarized light emitted from a 10" 7 M solution of fluorescein in PBS excited with horizontally polarized light of the same wavelength as used for the SCM measurementε. For the meaεurementε reported herein, G = 0.42. The P value of εtimulated lymphocyteε, that iε those lymphocytes that have been exposed to the general SCM-associated cancer recognition factor of the present invention, is compared with the P value of a control suspension of unstimulated lymphocytes from the same donor and the percent decrease in P value of the stimulated lymphocytes as compared to the P value of the control lymphocytes iε an indication of the SCM-response to the cancer antigen. Although the SCM reεponεe can be observed through some range of excitation and emisεion wavelengths, when using FDA as the fluorogenic agent precursor, it is strongly preferred to use an excitation wavelength of 470 nm and an emission wavelength of 510 nm. All results hereinafter described were obtained using those wavelengths. However, good results have also been achieved using an excitation wavelength of 442 nm and an emission wavelength of 527 nm. The spectrophotometer utilized for SCM fluorescence measurements should be one of high senεitivity and εtability and should be able to compensate for fluctuations in the intensity of the exciting light since the intensity of the polarized fluorescence emisεions is recorded as a function of time and since the bulk concentration of fluorescein in the SCM measurements is only of the order of 10" 8 M to 10" 9 M. Alεo, broad band filter inεtrumentε are not εuited for uεe for SCM measurements since SCM responses can be detected only within a narrow wavelength region. The maximum spectral slit width of the excitation monochromator should be 20 nm and the maximum spectral slit width of the emission monochromator should be 10 nm when the excitation monochromator is set at 470 nm and the emission monochromator at 510 nm. The spectrophotometer should also be fitted with a thermostatically controlled cuvette holder since the polarized fluorescent emisεions are highly temperature dependent. The spectrophotometer should also be provided with means for measuring both the horizontal and vertical polarized components of the fluorescent emisεionε. In the exampleε hereinafter set forth we used a Perkin-Elmer MPF-4 spectrophotometer which was equipped with a thermostatically controlled cuvette holder. All measurements were carried out at 27°C. The light source was a xenon lamp. In meaεuring the fluorescence polarization, the intensities of the emissions parallel to and perpendicular to the vertical exciting light beam are recorded alternately with an automatic polarizer changer for about 6 minutes or until the intensity of the emission perpendicular to the vertically exciting light beam reaches 80-90% of the full scale deflection of the recorder. It is neceεsary to correct these readings for any leakage of fluorescein from the cells and for any background of fluorescence in the substrate solution. To perform thiε correction, the cells are filtered away from the solution on a nitrocellulose filter of 0.22 μm pore size mounted in an appropriate filter head. Using the same fluorescence polarization measurement apparatus, the fluorescence intensities parallel to and perpendicular to the exciting light are obtained. The corrected fluorescein intensities for the cells are then obtained by subtracting the values obtained from the filtrate from the total fluorescence intensities extrapolated to the half time of filtration. This extrapolation is neceεεary becauεe the background increaεeε during the incubation becauεe of the leakage of fluoreεcein from cells and spontaneous hydrolysiε of FDA. Alternatively, the method of compenεating for background fluoreεcence described in the prior patent application by the Cerσeks, Serial No. 07/222,115, filed July 20, 1988, entitled "Method for Measuring Polarization of Bathochromically Shifted Fluorescence," and incorporated herein by this reference, can be used. Briefly, this method eliminates the need to filter each sample by measuring the horizontally and vertically polarized fluorescence emissions at more than one wavelength and calculating the intracellular fluorescence emissions therefrom. An SCM test performed according to the protocol described hereinabove, using 1.0 ml of a lymphocyte suspension at 6 X 10 6 cells/ml and 0.1 ml of the mitogen or antigen, with FDA as the fluorogenic agent precursor and using an excitation wavelength of 470 nm and an emission wavelength of 510 nm, is referred to herein as a "standard SCM test." b. Interpretation of the SCM Test The result of the SCM test iε a value for the intracellular fluoreεcein fluorescence polarization of the challenged lymphocytes. This value is designated aε a P value. The higher the measured P value, the greater the degree of polarization. The term "P s " is used to refer to the P value of an aliquot of lymphocytes that has been challenged with a challenging agent such as an SCM factor of the present invention. Similarly, the term "P c " is used to refer to the P value of an aliquot of lymphocytes not challenged with a challenging agent. When P s is compared with P c , a ratio of P s to P c of lesε than about 0.9 is an indication of the presence of malignancy in the body of the donor of the challenged lymphocytes. A preferred method of using the SCM factor aε a challenging agent in the SCM test comprises comparing P s to the fluorescence polarization value, P H of another aliquot of the lymphocytes contacted with a mitogen such as phytohaemagglutinin (PHA) , to determine an SCM response ratio, RRs CH , where RRs CH = P s ÷ P H . An RRs CH of less than about 0.9 indicates the presence of a malignancy. The use of the Rs CH is preferable because lymphocytes from donors free of malignancy respond to PHA but not to cancer-asεociated SCM factors, while lymphocytes from donors with malignancy do not respond to PHA but do respond to cancer-associated SCM factorε. This double change in responεe pattern giveε a sharper indication of the presence of a malignancy. B. Immunochemical Uses of the SCM Factors As discuεεed above, antibodieε can be produced against SCM factors by immunizing antibody-producing animals either with the SCM factors themselves or SCM factors conjugated to carrier proteins such as keyhole limpet hemocyanin (KLH) . These antibodies can be used for a number of immunochemical reactions, including aεεayε of SCM factor in body fluids, detection of cancer cellε in biopsies or aspirates by fluoreεcence microscopy or flow cytometric methods, and for other purposes discussed below under "Use of the SCM Factor in the Management of Cancer." 1. Immunoaεsavs for SCM Factor Once antibodies to SCM factor are produced, either monoclonal or polyclonal, they can be used in any type of immunoassays including: competitive or non- competitive sandwich immunoasεays; colorimetric assayε (e.g., ELISA, PGLIA (proεthetic-group-label immunoaεεay) , SLIFIA (εubεtrate-labeled fluoreεcence immunoassay) , etc.); radiometric procedures such as radioimmunoassay (RIA);.and asεayε employing lumineεcence, including both direct and catalyzed chemilumineεcence. The direct chemilumineεcence procedureε can uεe luminophoreε εuch aε acridinium derivatives; the catalyzed chemiluminescence procedures can use either enzymic, such as horseradish peroxidase (HRP) or other enzymatic or non-enzymatic catalysts, including metals. A large number of immunoasεays are known in the art and have been εummarized in M. Oellerich, "Enzyme-Immunoassay: A Review," J. Clin. Chem. Clin. Biochem. 22. 895-904 (1984) and C. Blake & B.J. Gould, "Use of Enzymes in Immunoassay Techniques," Analyst 109. 533-547 (1984), both of which are incorporated herein by this reference. For all of these types of immunoaεεays except immunoaεεayε dependent on aggregation of antigen-antibody complexeε, monovalent fragmentε of antibodies, such as Fab or Fab' fragmentε can substitute in some applications for entire bivalent antibody molecules. One particularly useful type of enzyme-linked immunoassay is the enzyme-linked immunosorbent aεsay (ELISA assay) . An ELISA assay for detection of SCM factor is described below in Example 21. Briefly, this assay entails: (1) attachment of SCM factor to a solid phase, typically plastic; (2) addition of sample to be assayed; (3) incubation of the solid phase with rabbit anti-SCM factor antibody; (4) incubation with goat anti- rabbit IgG antibody labeled with the enzyme alkaline phosphatase; (5) addition of p_"* n itrophenyl phosphate, a subεtrate for alkaline phoεphatase; and (6) measurement of absorbance at 405 nm. In this procedure, only the alkaline phosphatase bound to antibody attached to the solid phase will yield color; the greater the quantity of SCM factor in the sample, the lower the absorbance measured at 405 nm. The ELISA test can be used to detect the level of SCM factor in ultrafiltrates of blood plaεmaε (Example 23) , the presence of SCM factor in purified preparations from serum-free supernatant cancer cell media (Example 25) , and the presence of SCM factor in cultured human cancer cells (Example 26) . Because of potential crosε-reactivity of anti- SCM antibodies with α-l-PI because of the sequence homology between them, these immunodiagnoεtic tests are preferably carried out on body fluids from which α-l-PI melecules have been removed. The α-l-PI moleculeε can be removed by a number of techniqueε including, but not limited to, ultrafiltration through filters with nominal molecular weight cutoffs of 1,000 to 3,000 daltons, by passage through chromatographic columns, or by binding of α-l-PI to immobilized proteases such as trypsin, with which α-l-PI forms a stable complex. 2. Detection of Cancer Cells in Biopsies and Aspirates by Fluorescence Microscopy or Flow Cytometric Methods Anti-SCM antibodies labeled with fluorescent markers can be used for detection of cancer cells producing SCM in biopsies or aspirates by standard fluorescence microscopic and flow cytometric methods. C. Detection of SCM-specific Receptors It is believed that the effects of SCM factor on SCM-reεponding lymphocytes are mediated by the specific binding of SCM factor to SCM-factor-specific receptors located in the cell membrane of the lymphocytes. These receptors can be detected by the use of labeled SCM molecules, such as radiolabeled SCM factor, fluoreεcence-labeled SCM factor, enzyme-labeled SCM factor, or SCM factor labeled with a chemilumineεcent label. Alternatively, SCM factor can be conjugated to biotin. Avidin or streptavidin can then be labeled with enzymeε, fluoreεcent labels, or radioactive labels. The labeled avidin or streptavidin can be used to bind the biotin-conjugated SCM factor for labeling. D. DNA Sequences and Vectors 1. Design and Synthesis of Oligonucleotide Sequences The determination of amino acid sequences for both isolated and purified SCM factors, as well as the known amino acid εequence of the synthetic SCM factor, allows the construction of DNA oligonucleotide sequences corresponding to these amino acid sequenceε. The construction of these oligonucleotide sequenceε varieε somewhat depending on whether their desired use is to be expressed in an in vitro expresεion εyεte or to detect the natural gene or genes for SCM factor present in the DNA of the human genome. However, in either case, the oligonucleotides are synthesized according to well-known techniques, such as the phosphotrieεter method or the phosphite triester method, as described in K. Itakura, J.J. Rosεi, & R.B. Wallace, "Syntheεiε and Uεe of Synthetic Oligonucleotideε," Annu. Rev. Biochem. 53. 323 (1984) . a. Sequences for Expression If the ultimate use of the εequence is to be for the production of genetically-engineered SCM factor by expression in an in vitro system, then it is only necessary to synthesize one DNA sequence corresponding to any particular amino acid sequence. However, the genetic code is degenerate, and the use of different codons for the same amino acid affects the rate of translation of the sequence in the host cell. It is desirable to select codons for those amino acidε for which there iε a choice according to the preferred codonε for tranεlation in the particular hoεt organiεm from which the expression system used is derived. Becauεe codon uεage varies as between bacteria and eukaryoteε, it is desirable to vary the exact εequence of the DNA according to the host in which the DNA sequence is to be expressed. The differences in codon usage between bacteria and mammals, including humans, are well-known in the art. b. Sequences for Detection If the synthesized DNA sequence is to be used to detect the natural genes for SCM factor in DNA, different conεiderations enter into the selection of the nucleotide sequence. To obtain accurate hybridization, it is frequently desirable to use a multiplicity of sequenceε εo that all poεεible sequences corresponding to the desired amino acid sequence are present. As one possible example, the region between amino. acids 14 and 22 is nearly invariant in the synthesized as well as in the purified SCM factors, being either F-L-M-I-D-Q-N-T-K or F-L-M-I-E-Q-N-T-K. If all possible codon combinations were used, however, there would be 2,304 27-nucleotide- long sequences that could correspond to these amino acid sequences. This number of different sequenceε iε too great to handle efficiently in a hybridization reaction, εo a poεεible compromiεe is to eliminate codons that are the least likely to be used in human DNA, according to R. Lathe, "Synthetic Oligonucleotide Probes Deduced from Amino Acid Sequence Data: Theoretical and Practical Conεiderationε," J. Mol. Biol. 183. l (1985). For example, if the three codonε least likely to be used are eliminated for leucine, the single least used codon eliminated for isoleucine, and the two least used codons eliminated for threonine, there would be a posεible total of 384 εeparate 27-nucleotide-long sequences. This number of εeparate sequences has been used, for example, in R.B. Wallace, M.J. Johnson, T. Hirose, T. Miyake, E.H. Kawashima, and K. Itakura, "The Use of Synthetic Oligonucleotideε aε Hybridization Probes. II. Hybridization of Oligonucleotides of Mixed Sequence to Rabbit /S-Globin DNA," Nucl. Acids Res. 9. 879-894 (1981). 2. Incorporation of DNA Sequences Into Vectors Vectors for transfection or transformation contain the DNA sequence coding for the SCM factor and control sequences εuch aε promoterε and enhancers operatively linked to the coding εequences. The vectors also contain suitable replication sites. Both the control sequences and the replication sites are active in the intended host strain. When the host strain is the bacteria Escherichia coli. plasmids such as pBR322 are suitable vectors. When the host strain is a cultured mammalian cell such as a human cell, the vector is typically a viruε εuch aε SV40. Suitable host-vector syεtemε are well-known in the art and are deεcribed, for example, in B. Perbal, "A Practical Guide to Molecular Cloning" (2d ed. , John Wiley & Sons, 1988) and "Guide to Molecular Cloning Techniques" (S.L. Berger and A.R. Kimmel, eds., Academic Presε, 1987; Volume 152 of Methodε in Enzvmology) . Techniques for incorporation of the desired sequences into the vectors by ligation, for tranεfection or tranεformation of the hoεt cellε with the ligated vectors, for propagation and selection of the host cells containing the vectors, and for the expression of the SCM factor coded for by the DNA sequences are all well-known in the art and are described in the Perbal or Berger & Kimmel references, supra. IV. RELATIONSHIP BETWEEN THE SCM FACTOR AND CANCER A. Protection of Cancer Cells in Vivo by SCM Factor SCM factor molecules are now known to be εyntheεized by cancer cellε. The SCM factor gene could be the result of genetic damage caused by chemical or viral agents, or it could be an oncogene whose normal counterpart is present in the cell. Like other known α- 1-PI variants, the SCM factor gene or genes are likely derepresεed by tumor-inducing agentε and expreεεed when the mechanisms regulating cell division are activated by tumor promoters. Proteaseε and their inhibitors are closely implicated in the regulation of cell replication, division, maturation, and fertilization procesεeε. A genetic defect causing production of a functionally abortive part of the α-l-PI molecule could contribute to the erratic and uncontrolled proliferation of initiated and promoted cancer cells. Our resultε εuggeεt that SCM factor molecules can protect cancer cells and enhance their metastatic spread in several ways: stimulating DNA syntheεis of cancer cells (Example 27) , protecting the activity of cancer-cell-asεociated proteaεeε (Example 28) , and circumventing the immune εurveillance and other anti-tumor responseε of the hoεt. One particular protective effect iε the εuppreεεion of natural killer (NK) activity of lymphocyteε by the SCM factor (Exampleε 13 and 31) . Another poεεible protective effect iε εcavenging the reactive oxygen-containing species released by macrophages against cancer cells via the methionine residues incorporated in the SCM factor sequence. Another indication of the common origin of α-1- PI and the SCM factor, as well as the homology between them, is our discovery that a protein present in the 50 to 100 kilodalton molecular weight fraction of blood plasma in donors both having cancer and free of cancer can modify or abolish the SCM response to the SCM factor in the SCM-responding subpopulation of lymphocytes from cancer patients. This protein can also restore the SCM responεe to PHA in theεe cells. This SCM response modifying factor was originally designated as "plasma factor 2" (PF2) . Incubation of SCM-responding lymphocytes from cancer patientε for 2.5 hours in the presence of the 50 to 100 kilodalton molecular weight fraction of plasma from allogeneic or autologous donors removes, on subsequent washing of the lymphocytes, the receptors for cancer-associated factors, including SCM factor, and restores the ability of these lymphocytes to respond again to PHA. That is, the protein reverts the RR $CM f rom values typical of lymphocytes from donorε with cancer (leεs than 1) to valueε typical of lymphocyteε from donorε free of cancer (greater than 1) . PF2 protein, unexpectedly, iε identical with α-l-PI (Example 29) . The α-l-PI protein can reverεe the SCM reεponse of normal lymphocytes that have been treated with SCM factor, and can also reverse the SCM response of lymphocytes from donors afflicted with cancer. B. Use of the SCM Factor in the Detection and Management of Cancer As previously detailed in our patent application Serial No. 07/167,007, the SCM factor of the present invention can be used for a number of purposes both in the detection and in the management of cancer. 1. Detection of Cancer a. Use of SCM Factor as Challenging Agent SCM factor, or any of its active fragmentε, can be used as a challenging agent in the SCM test for the detection of cancer. Lymphocyteε from donorε with cancer, but not from donors free of cancer, are primed to respond to cancer-asεociated factorε in the SCM teεt. Accordingly, only lymphocyteε from donors with cancer respond to SCM factor with a decrease in intracellular fluorescein fluorescence polarization value in the SCM test. Thiε reεponεe conεtituteε an early warning that cancer cellε producing SCM factor are preεent in the body of the lymphocyte donor, even when the number of tumor cells or the size of the tumor might not be otherwise detectable. b. Detection of Receptors Specific for SCM Factor SCM factor molecules or fragments that are labeled can be used to detect the presence of receptorε for SCM moleculeε on the SCM-reεponding fraction of lymphocytes. The label can be, but is not limited to, a radioactive label, a fluorescent label, a chemiluminescent label, or an enzyme label. The preεence of theεe receptors is itεelf an indication of cancer. They can be detected using flow cytometry, fluorescence microscopy, enzyme-linked aεεays, or other assays for lymphocyte receptors. If the SCM molecules are labeled with radioactive isotopeε, autoradiography, scintigraphy, and other detection methods for radionuclides can be used to detect the presence of receptors for SCM factors. If SCM-responding lymphocytes are isolated, washed, and incubated with a saturating quantity of labeled SCM factor, the extent of the binding of the SCM factor to the lymphocytes indicates the number of SCM factor receptors present per lymphocyte. This test can be used to indicate the senεitization of SCM-responding lymphocytes to the SCM factor and can be used as an alternative to the SCM test to detect the preεence of cancer; it can alεo be uεed to confirm the findingε of the SCM test. c. Detection of SCM Factor Molecules in Cancer Biopsies By flow cytometry, fluorescence microscopy, or enzyme-linked assays, SCM factor molecules can be detected in cancer biopsies using appropriately labeled anti-SCM factor antibodies. Because SCM factor molecules are produced in quantity by cancer cells, their presence in biopsy specimenε iε a strong confirmation of the cancerous nature of the tissues from which the biopsy specimen is taken. d. Detection of SCM Factor Molecules in Body Fluids As shown above, SCM factor molecules are excreted by cancer cells into body fluids such as blood plasma or urine. The preεence of SCM factor in body fluids can therefore be used as a general cancer-specific marker. The presence of SCM factor moleculeε can be detected in ultrafiltrateε of cancer patientε' blood plaεma uεing antibodieε against SCM factor in the immunoassayε described above under "Immunoasεayε for SCM Factor"; either polyclonal or monoclonal antibodies of sufficient specificity can be used in the immunoassays. Antibodies to fragments of the SCM factor can substitute for antibodies to the entire SCM molecule in many applications. As the production of SCM factor molecules by cancer cells is decreased by inhibitors of protein syntheεiε, the concentration levels of SCM factor in body fluids can be used to indicate the metabolic activity of any remaining cancer cells following treatments, and to detect the recurrent growth of cancer or the presence of otherwise occult metastaεeε. The preεence of SCM molecules could in addition serve as a warning that cancer cells present in the body of the patient are likely to metastasize. 2. Treatment of Cancer As detailed above, the SCM factor protects cancer cells against normal defense mechanisms and promotes their growth and spread. The mechanism by which the SCM factor accomplishes this includes, but is not limited to, protection of cancer cellε from the action of natural killer (NK) cells (Examples 13 and 31) . Thiε effect of SCM factor leads to the idea that measures that selectively decrease the in vivo activity of the SCM factor can be useful in the management of cancer. As a firεt εtep of εuch methods, once lymphocytes from a known or εuεpected cancer patient have been εhown to give a poεitive reεponεe in the SCM test with the SCM factor of the present invention as a challenging agent, a sample of a body fluid can be taken from the patient, pasεed through an ultrafilter with a nominal molecular weight cutoff of 1,000 daltons, and the fraction passing through the ultrafilter collected and used as an autologous cancer factor to challenge lymphocytes from the same patient in the SCM teεt to confirm the presence of the SCM factor in the fraction. It need not always be necessary to perform this confirmatory test, particularly if other clinical indicators indicate the presence of cancer. a. Inactivation of SCM Factor in Body Fluids Once the presence of SCM factor in a body fluid of a cancer patient is shown or inferred, the body fluid can be treated by one of several methods to reduce the in vivo effect of the factor by inhibiting its production, selectively removing it, or selectively inactivating it, and the body fluid can then be returned to the patient, thereby enhancing the resistance of the patient to the malignancy. Since the SCM factor of the present invention causes a response in the SCM test regardless of the type of cancer afflicting the patient, it is believed that reducing the in vivo effect of the SCM factor can enhance the resistance of the patient not only to the particular type of cancer originally diagnosed, but also to any other type of malignancy that might subsequently develop in the patient. This can prove εignificant when treating patientε with drugε that have an immunosuppressant effect, or patients with an already compromised immune system due to conditions such as AIDS. (1) Inactivation bv Dialysis When the body fluid is peripheral blood, one method of reducing the in vivo activity of the SCM factor is to physically remove it by dialysis of the peripheral blood to remove peptides with an apparent molecular weight of 1,000 daltons or less, since the factor will pass through ultrafilters with a nominal molecular weight cutoff of 1,000 daltonε or leεε, even though itε actual molecular weight iε somewhat greater. (2) Inactivation bv Reaction with Antibodies or Antisense Peptides Another method of reducing the-, in vivo activity of the SCM factor in a body fluid is to neutralize it or inactivate it with antibodies specific for the factor. The antibody is prepared as described above and can be polyclonal or monoclonal. Alternatively, monovalent antibody fragmentε, εuch as Fab fragments or Fab' fragments, can be used. Use of monovalent fragments can be preferable to use of intact antibody in some applications if the formation of large SCM factor- antibody complexes is considered undesirable. The presence of such large antigen-antibody complexes in the peripheral blood can possibly cause serum sickness and other allergic reactions. As an alternative to the use of antibodieε, antiεenεe peptideε encoded by the antiεenεe strand of the DNA whose senεe strand encoding for SCM factor can also be used to inhibit the activity of SCM factor. Aε reported in Y. Shai, T.K. Brunck, & I.M. Chaiken, "Antisenεe Peptide Recognition of Sense Peptides: Sequence Simplification and Evaluation of Forces Underlying the Interaction," Biochemistry 28. 8804-8811 (1989) , and G. Fasεina, M. Zamai, M. Brigham-Burke, & I.M. Chaiken, "Recognition Propertieε of Antiεenεe Peptides to Arg 8 -vasopressin/Bovine Neurophysin II Bioεynthetic Precurεor Sequences," Biochemistry 28. 8811- 8818 (1989) , peptides that are encoded by the antisense strand of a DNA molecule whose εenεe εtrand encodeε a phyεiologically active peptide often .interact εpecifically with that peptide. The "εenεe strand" is _ the strand of the DNA identical in sequence with the mesεenger RNA corresponding to it (except for the subεtitution of U in mRNA for T in DNA) , while the "antiεenεe εtrand" is complementary to the sequence of the mRNA. For example, if the sense strand has the sequence ATG, the antisense strand would have the sequence CAT. As applied to inhibition of SCM factor, the antisense peptide has an amino acid sequence encoded by the antisense strand of a DNA sequence whose sense strand encodes a cancer recognition factor of at least 9 amino acid residues including a core sequence of 9 amino acid residues having an amphipathicity profile substantially equivalent to the sequence F-L-M-I-D-Q-N-T-K. Typically, the cancer recognition factor has the amino acid sequence F-L-M-I-D-Q-N-T-K, corresponding to residues 14-22 of the synthetic SCM factor molecule, or the sequence M-I-P-P-E- V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K, corresponding to the entire synthetic SCM molecule. b. Tagging Anti-SCM Factor Antibody with Anti-cancer Substances Because SCM factor is produced by actively metabolizing cancer cells (Examples 25 and 26) , an antibody specific for the SCM factor can be used to target an anti-cancer subεtance to εuch cellε by labeling anti-SCM factor antibody with the anti-cancer εubεtance. This directs the anti-cancer substance to the site of the cancer and thereby raises the effective concentration of the anti-cancer substance at the site of the cancer. This procedure can be especially advantageous when the anti-cancer subεtance iε one that produceε εide effects when given in larger doses. Such labeling can be performed by standard conjugation procedures used for conjugating enzymes, fluorescent labels, or radioactive labels to antibodies as described in P. Tijssen, "Practice and Theory of Enzyme Immunoaεεay ," (Elsevier, Amsterdam, 1985), pages 221-278. c. Use of Non-homologous Protease Inhibitors Effective control of the proliferation and invasive spread of cancer cells enhanced by SCM factor might be achieved by inhibition of the proteases that are protected against natural inhibitors by the SCM factor by using natural inhibitors that are non-homologous with the SCM factor but of the εame εmall size and ease of diffusion. Preferably, the inhibitor is non-homologous with any other protease inhibitor that is subεtantially inhibited by SCM factor. Examples include the synthetic variant of Cucurbita maxima trypsin inhibitor, a 29- reεidue peptide. Such natural or εynthetic proteaεe inhibitorε εhould be selected for their ability to overcome the protective effect of the SCM factor. Screening of such potential protease inhibitorε εhould therefore be carried out on proteases protected by the SCM factor, either by the entire SCM factor or by the portion of the molecule active in inhibition of α-l-PI, the amino-terminal seven residues. We suggest that the use of such protease inhibitors non-homologous with α-1- PI and capable of inhibiting proteases in the presence of SCM factor could be used for cancer treatment. The simultaneouε removal of SCM factor from blood plasma by dialysis might help to diminish its effect on the patients' defense mechaniεms. d. Use of Inhibitors of Protein Synthesis to Inhibit SCM Factor Formation Because SCM factor iε the result of active protein synthesis by cancer cells, new εyntheεiε of SCM factor can be decreased by treatment with suitable clinically acceptable non-toxic inhibitors of protein syntheεiε that causes a decrease in production of SCM factor by tumor cellε, εuch as cycloheximide or ascorbic acid. We have previously demonstrated that ascorbic acid can selectively induce the transition of mitochondria into the idling, orthodox conformation in cancer cellε, thereby decreaεing their metabolic activity. Example 30 _ _ shows the effect of ascorbic acid on the syntheεiε of SCM factor in MCF7 human breast cancer cells in culture. Addition of 10 "3 M ascorbate decreaεed the εyntheεiε of SCM factor in theεe cellε conεiderably as measured by the ELISA procedure using anti-SCM antibodies. The use of ascorbic acid or other protein synthesis inhibitors is therefore proposed as a cancer-specific, non-toxic inhibitor of SCM factor synthesis. It could be used on its own or in conjunction with other methods of removing or inactivating SCM factor. e. Reversing NK-Suppressive Action of SCM Factor Because the NK-suppresεive activity of SCM factor is believed to protect cancer cells from natural defenses, one way of restoring the effectiveness of those defenseε iε by reverεing the NK-εuppreεsive effect of SCM factor. Such a method can comprise administering to a patient at least one of whose body fluids contains SCM factor a SCM-factor-inhibiting εubεtance in a quantity sufficient to substantially reverse the NK-suppreεεive action of the SCM factor and εubεtantially reεtore normal NK activity of lymphocyteε of the patient aε measured by in vitro lysis of K562 cells by the lymphocytes. The SCM-factor-inhibiting substance can be antibodies to SCM factor, univalent antigen-binding fragments of antibodies to SCM factor, or antisenεe peptides whose amino acid εequences are those encoded by the antisense strand of DNA sequences whose sense strand encodes a NK-suppresεive peptide sequence. 3. Use of Anti-SCM-factor Antibodies to Image Cancer Cells Because the SCM actor is produced by cancer cells and is found in association with them, anti-SCM- factor antibodies can also be used to image cancer cells by labeling the antibodies with imaging substances such as fluorescent dyes or radioactive isotopes. Such labeled antibodies can be used to detect cancer cells in biopsies by fluorescence microscopy or autoradiography. Fluorescent-labeled antibody can also be used for automated detection of cancer cells by flow cytometry. 4. Use of SCM Factor to Modulate Immune System Activity Because the SCM factor iε capable of inhibiting the NK activity of lymphocyteε (εee Exampleε 13 and 31) , it can be uεed to modulate immune εyεtem activity and assess the effectivenesε of anti-cancer drugε. Example 31 shows that the NK-suppressive activity of SCM factor is present only in the entire synthetic SCM factor molecule (29 amino acids) and fragment F2 (amino acids 8- 29 of synthetic SCM factor) . Peptides derived from fragment F2 but incorporating one or more conservative amino acid substitutions are also expected to have NK- εuppreεεive activity. Such peptides having NK-suppresεive activity can be uεed in a method for aεεeεεing the effectiveneεε of an anti-cancer agent capable of inhibiting the growth of malignant cellε in a cell culture. The cell culture includeε both lymphocyteε exhibiting NK activity and malignant cellε. The method compriεeε the εtepε of: (1) incubating the cell culture with a εubstantially purified NK-suppressive peptide in a quantity sufficient to substantially suppress the NK activity of the lymphocytes of the cell culture; (2) adding the anti-cancer agent to the cell culture in a quantity sufficient to inhibit the growth of the malignant cells; and (3) determining the effect of the anti-cancer agent on the malignant cells by measuring the inhibition of growth of the malignant cells in the esεential abεence of NK activity of the lymphocyteε. Such NK-suppreεεive peptideε can alεo be uεed in a method of εuppreεεing the NK activity of lymphocytes. The method comprises administering to the lymphocytes a εubεtantially purified NK-εuppreεεive peptide in a quantity εufficient to εubstantially suppreεε the NK activity of the lymphocyteε aε meaεured by a standard test for NK activity. Such a standard test is the in vitro lysis of K562 cellε. Thiε method of εuppreεεing NK activity can be useful when it is desired to modulate immune syεtem activity. A clinical example in which such modulation is desirable is the transfusion of blood into patients who have just undergone a tissue transplant and are at risk of rejection of the transplant; the lymphocyteε of such blood can be treated with the NK-suppressive peptide to diminish the risk of such transplant rejection. Similarly, a substantially purified SCM factor or NK-suppreεεive peptide can be used aε an immunoεuppreεεive drug. The method of uεe comprises administering an immunosuppressive fraction alone or in combination with a pharmaceutically acceptable carrier in a quantity sufficient to create a degree of immunosuppreεεion capable of enhancing allograft εurvival. The immunoεuppressive fraction can be a substantially purified naturally occurring SCM factor, the 29-amino-acid synthetic SCM factor, or a NK- suppressive peptide that includes at least residueε 8-29 of the εynthetic SCM factor or iε derived from that sequence by the occurrence of conservative amino acid subεtitutionε. EXAMPLES The following Examples illustrate: (1) the iεolation, purification, characterization, and activitieε of εubεtantially purified SCM factor from body fluids of patients with cancer and (2) the characterization and activities of synthetic SCM factor and peptides comprising partial sequences of synthetic SCM factor. These Examples are for illustrative purposeε only and are not to be conεtrued aε limiting the invention. Example 1 Initial Purification of the General Cancer-Aεεociated SCM Factor from Blood Plasma Blood sampleε from patientε positively diagnosed as having active cancer, such as cancer of the breast, lung, colon, ovary, cervix, uterus, larynx, or skin (basal cell carcinoma and malignant melanoma) were collected into heparinized vials such aε Vacutainer™ tubeε. Twenty-milliliter portions of the blood samples were centrifuged at about 1200 xg. for approximately 40 min. The plasma above the sedimented blood cellε was collected and filtered by pressure through a porous membrane filter such as an Amicon™ UM2 or YM2 filter, with a 1000-dalton molecular weight cutoff. These ultrafiltrates were lyophilized or stored at 4°C until further purification. Example 2 SCM Activity of Initially Purified SCM Factor from Example 1 Aliquots of the ultrafiltrate from each εample of Example l were incubated with potentially SCM- reεponding lymphocyteε obtained from the sane donors and the lymphocytes checked for their SCM responεe in accordance with the SCM teεt procedure deεcribed above. In every case the ultrafiltrate caused the SCM-responding lymphocytes to respond characteristically with a decrease in P value, as they would have if they had been contacted with the cancerous tissue itself or with extractε of cancerouε tissue (Table 1) . TABLE 1 SCM ACTIVITY OF ULTRAFILTRATES OF EXAMPLE 1 Diagnosis of Diagnosis of SCM Response: Lymphocyte Donor SCM Factor Donor P Value as % of Control Malignant Melanoma Malignant Melanoma 75.7 Malignant Melanoma Basal Cell Carcinoma-Skin 82.0 Ca-Larynx Ca-Larynx 62.9 Ca-Breast Ca-Breast 76.0 The data of Table 1 show that even when present in the crude ultrafiltrate, the SCM factor caused a decrease in the P value of the SCM-responding lymphocytes from donorε afflicted with cancer at leaεt equivalent to the decreaεe of the P valueε obεerved when lymphocyteε are εtimulated by crude extractε of cancerouε tissues or cancerous tissues themselves. The decrease in P value on stimulation by the ultrafiltrates was at least 10%, which is characteristic of εuch a positive SCM response. However, the SCM factor did not pass through the Amicon™ UM05 filter with a nominal 500-dalton molecular weight cutoff. These data confirm the small size of the factor while indicating that the activity is larger than a small molecule such as a single amino acid. Example 3 Further Purification of the SCM Factor of Example l The lyophilized powder from the samples of Example 1 was disεolved in 2 ml of εterile preservative- free water for injections. At this stage, the SCM activity of the preparations was ascertained, and active sampleε from donors with the same type and site of cancer were pooled. The pooled sampleε were deεalted on an 0.9 X 18 cm column of Sephadex™ G-10, which haε a fractionation range of from 0 to 700 daltonε. The εample volume per column chromatographic run did not exceed 25% of the column volume. Elution waε carried out with double diεtilled water at the linear elution εpeed of 8 to 9 cm/hr. The deεalting was carried out at room temperature (21°-23°C). One-ml fractions eluting at between 0.3 and 0.5 times the total chromatographic bed volume were collected and the optical densities of the fractions determined. The SCM activity was contained within the first elution peak. The presence of SCM activity in that peak was confirmed by an SCM test. An aliquot of the first elution peak, prepared from an ultrafiltrate originally derived from plasma of a patient with breast cancer reduced the P value of lymphocytes from a patient with breast cancer to 86.3% of the control value in the SCM test, indicating the presence of SCM activity. These fractionε were collected and lyophilized. The eluate waε further purified by fractionation on a Sephadex™ G-50 gel filtration column, which haε a fractionation range of from 1500 to 30,000 daltons. The lyophilized desalted samples were dissolved in 50 mM NH 4 HC0 3 , loaded at no more than 5% of the column volume on a 0.9 X 18 cm Sephadex G-50 column at the linear elution speed of 3 cm/hr. The elution was carried out at room temperature, and one-milliliter fractions eluting from the column at between 0.4 and 0.6 timeε the total chromatographic bed volume were collected. Theεe fractions were tested for SCM activity. Results of these testε are given below in Example 4. The SCM-active fractionε were contained within the firεt elution peak as determined by optical densities of the one-milliliter fractions after testing of the fractions in the SCM test. Once the fractions were teεted for SCM activity, the active fractionε from the εame cancer types were pooled and lyophilized. For further purification the lyophilized samples were dissolved in 10 mM NH 4 HC0 3 and loaded at no more than 4% of the column volume on an 0.8 X 26 cm column of Whatman DE-52 microgranular DEAE-cellulose. The column was washed with 10 ml of 10 mM aqueous NH 4 HC0 3 increasing by 0.108% per minute from 10 mM to 1 M NH A HC0 3 . One-milliliter fractions were collected and the optical absorption at 220 nm was determined for each fraction. Based on the optical absorbance, active fractions eluting from the column at between 4.5 and 4.7 timeε the total chromatographic bed volume were pooled and lyophilized for teεting and further purification. Reεults from SCM testing of the active fractions are given in Example 4. Example 4 SCM Activity of Further Purified Preparations of Example 3 Table 2 εhowε the results when aliguots of the Sephadex G-50 fractions from Example 3 originally from donors with variouε typeε of cancer were uεed to challenge lymphocytes from donors, also with various types of cancer, in the SCM test. It can be seen that potentially SCM-responding lymphocytes have the same characteriεtic reεponεe to the G-50 fractionε aε they did to the previously characterized cancer-associated antigens. This desalted partially purified proteinaceous material exhibits a generally increased SCM response as compared to the crude ultrafiltrate for which the results were shown in Table 1. This increased SCM response is shown by decreased P values. TABLE 2 Table 3 shows the results when SCM factor obtained from donors with various types of malignancies after purification through the DEAE-cellulose stage was used to challenge lymphocytes isolated either from donors with various typeε of malignancieε or from donorε free of malignancy in the SCM test. As expected, the lymphocytes from cancer patients responded to the SCM factors purified from the DEAE-cellulose columns with a considerable decrease in P value, while lymphocytes from donors free of malignant disease showed no such decrease in P value. TABLE 3 SCM ACTIVITY OF DEAE-CELLULOSE FRACTIONS OF EXAMPLE 3 SCM Diagnosiε of Diagnoεiε of Response: Lymphocyte Donor SCM Factor Donor P Value as % of Control Ca-Breast Ca-Breast 69.2 Ca-Breast Ca-Bronchus 69.5 Ca-Breast Ca-Cervix 69.0 Basal Cell Basal Cell Carcinoma-Skin Carcinoma-Skin 82.0 Healthy Donor Ca-Colon 98.6 Cholecystitiε Malignant Melanoma 100.0 Urethritiε Ca-Cervix 99.8 Appendicitis Ca-Colon 98.0 Benign Breast Growth Ca-Breast 97.8 Benign Pituitary Adenoma Ca-Brain 100.0 Example 5 Final Purification of SCM Factor of Example 3 by RP-HPLC The DE-52 general cancer-aεεociated SCM-active fractionε of Example 4 were then reconεtituted and purified to homogeneity by reverεe phase high presεure liquid chromatography (RP-HPLC) using a 2.1 mm X 22 cm HPLC column. The column was packed with Aguapore RP-300™ (7 microns) . The mobile phases used in the RP-HPLC purification step were aε followε: Phaεe A: 0.1 volume percent aqueouε trifluoroacetic acid (TFA) . Phaεe B: 0.09 volume percent aqueouε TFA in aqueouε 70% acetonitrile. Lyophilized DE-52 SCM-active fractions were reconstituted with sterile water for injections (without preservatives) and 250 microliter aliquots were injected into the RP- HPLC column. The mobile phase flow rate waε 50 microliters per minute and its composition profile was 10 minutes of 90 volume percent of Phase A, 10 volume percent of Phase B, followed by 30 minutes of linear increase of Phase B at the rate of 3 volume percent per minute. The optical density peaks detected by optical absorbance at 220 nm were hand-collected via a "nanobore" teflon tubing into 1.5 ml plaεtic conical Eppendorf centrifuge tubes and the solvent was evaporated in a vacuum centrifuge. In all caseε, the general cancer- associated SCM-recognition factor eluted from the column at 74 volume percent of Phase B. Example 6 Alternative RP-HPLC Purification of SCM Factor Alternatively, the SCM factor can be purified by performing HPLC using a 4.6 mm X 25 cm HPLC column packed with Ultrasphere ODS™ (5 microns) distributed by Beckman Instruments, Inc. with the DEAE-52 SCM-active fractions of Example 4. The mobile phases used with this column were as follows: Phase A: 0.1 volume percent aqueous trifluoroacetic acid (TFA) . Phase B: 0.1 volume percent TFA in aqueous 70% acetonitrile. The same general procedure was followed with this column as for the Aquapore column, except that the mobile phaεe flow rate was 1.00 ml per minute and its composition profile was 5 minutes of 70 volume percent of Phase A, 30 volume percent of Phase B, followed by 20 minutes of linear increase of Phase B at the rate of 3.5 volume percent per minute. The optical density peaks were detected at 220 nm and were hand-collected into εiliconized glass test tubes and the solvent was evaporated in a vacuum centrifuge. When thiε HPLC system was used, in all cases the purification of general cancer-associated SCM-recognition factor from nineteen different cancer types, including squamouε cell carcinoma of the cervix, adenocarcinoma of the breast, adenocarcinoma of the bronchus, and malignant melanoma, always yielded a single optical density peak of activity, eluting at 56.3 volume percent of Phase B. Example 7 SCM Activity of RP-HPLC Purified Preparations of Example 6 For SCM activity testing of the peptides iεolated by RP-HPLC on the Ultraεphere column in Example 6, the peptides were reconstituted with sterile water for injections without preservativeε. The SCM activity of SCM-reεponding lymphocytes after incubation with these samples is shown in Table 4. This fraction gives the greatest decrease in polarization value when uεed to challenge lymphocytes from donors afflicted with cancer. Two of the three preparations of SCM factor gave a decrease in polarization value greater than 40%, a larger decrease than seen with any other fraction tested. The purified factor, as expected, was non-specific with respect to the type of cancer afflicting the donor of the lymphocytes used. Also as expected, the purified factor gave no response when used to challenge lymphocytes from healthy donors. TABLE 4 Example 8 Identification and Isolation of SCM-Active Tryptic Peptides from SCM Factor Purified from Blood Plasma of Patients with Breaεt Cancer and Lung Cancer Tryptic peptides with SCM activity were isolated from the purified SCM factors isolated from blood plasma of patients with breast cancer or lung cancer. The cleavage of the purified factors with trypsin and purification of the active fragments were carried out by the following procedure: To prevent adsorption loss of the peptide during lyophilization, the SCM factor was digested with trypsin in the presence of HPLC eluantε. Trypεin digestion was carried out in 0.1 M Tris-HCl buffer, pH 8.3, at 37°C for 24 hours using 10 percent by weight of trypsin. The digeεt waε diluted fourfold with 0.1 volume percent aqueouε trifluoroacetic acid, and waε injected into an Applied Biosystems 130A microflow HPLC-separation system. The tryptic fragments were separated using an Aquapore RP-300 column (200 mm X 2.1 mm). For the elution of the fragments, the mobile phase solvents were: Phase A: 0.1 volume percent aqueous trifluoroacetic acid (TFA) . Phase B: 0.09 volume percent TFA in aqueous 70% acetonitrile. The mobile phase flow rate was 50 μl per minute and the composition profile was 10 minutes of 96 volume percent Phaεe A, 4 volume percent Phaεe B, followed by a linear elution gradient compriεing a 30 min linear increase in Phase B at a 3 volume percent per minute rate. The SCM- active tryptic peptide fragment eluted at 69.6 volume percent of Phase B and 30.4 volume percent of Phase A in a total volume of about 30 microliters. The tryptic peptide cleaved from the SCM factor purified from patients with lung cancer was tested for SCM activity in Example 10, below, and found to be fully active. By comparison with the sequences of the entire isolated SCM factors determined in Example 14, these tryptic peptideε were found to repreεent amino acids 8-22 of the SCM factor molecule. Example 9 Use of the Isolated SCM Factor as the Challenging Agent in the SCM Test Table 5 summarizes the results obtained by using preparations of the general cancer-associated SCM recognition factor at various stageε of purification from Exa pleε 1, 3, and 6 aε the challenging agent in the SCM test. When lymphocytes from donorε afflicted with a number of different malignancies were used with the factor of the present invention in the SCM test, a significant responεe waε εeen in all cases. This reεponse is given in Table 5 as a percent of the control polarization value obtained by performing the SCM measurement on the same lymphocytes unincubated with the factor. The smaller the value the greater the response to the factor in the SCM test. Even the crudest preparation of the factor tested, the ultrafiltrate, give a decrease in polarization value of from 18.0% to 37.1%, and the most highly purified fraction, purified by RP- HPLC, gave a decrease in polarization value of as great as 44.6%. The factor of the present invention is specific and only causeε a decreaεe in polarization value when uεed to challenge lymphocytes from donors afflicted with cancer. Even the RP-HPLC purified fraction caused no decrease in polarization value when used to challenge lymphocytes from healthy donors. TABLE 5 EXAMPLES OF SCM ACTIVITY AT DIFFERENT PURIFICATION STAGES (EXAMPLE 9) Range of Percentage Decrease Stage of Purification In P Value When Lymphocytes From Cancer Patients Used Ultrafiltrate of Plasma (1000-dalton Cutoff) 18.0 - 37.1 Sephadex G-50 Fraction 19.8 - 37.0 DE-52 Cellulose Fraction 18.0 - 31.0 RP-HPLC Fraction 32.0 - 44.6 No fraction showed any activity when tested against lymphocytes from healthy donors, or from donorε with non- malignant diseases. Example 10 Activity of the Tryptic Peptide of Example 8 in the SCM Test The tryptic peptide obtained from SCM factor from plasma of patients with lung cancer, whose purification was described above in Example 8, was fully active in the standard SCM test. Approximately 5 X 10 "2 femtograms of this fragment (i.e., 5 X 10 "17 grams, or approximately 16,000 molecules of the fragment) gave full activity in the test. When the fragment was isolated from patients with lung cancer, it proved active in the SCM test when tested against lymphocytes from a patient with small cell lung carcinoma, and crosεreacted fully with lymphocytes from a patient with adenocarcinoma of the breast, as shown in Table 6. However, no response was seen when lymphocytes from healthy donors were used. TABLE 6 SCM ACTIVITY OF TRYPTIC FRAGMENT OF EXAMPLE 8 FROM LUNG CANCER SCM Response: Diagnosis of Lymphocyte Donor P Value as Percent of Control Small Cell Lung Carcinoma 70.0 68.0 Adenocarcinoma of Breast 67.5 68.0 Healthy Donorε 102.0 104.0 _ Example 11 Cross-Reactivity of Iεolated SCM Factorε The following example demonεtrates the ability . of the isolated SCM factor to cause a response in the SCM test when used to challenge lymphocytes derived from donorε afflicted with diεεimilar typeε of cancer. In order to demonstrate this cross-reactivity, two milliliters of cell-free blood plasma was obtained from each of a number of blood samples from cancer patients. The blood samples had originally been collected into heparinized Vacutainer™ tubes. The samples were ultrafiltered through an Amicon™ UM2 or YM2 filter with a nominal molecular weight cutoff of 1000 daltonε for at least 12 hr and stored under sterile conditions at 4°C. Potentially SCM-responding lymphocytes were iεolated from heparinized blood εampleε from patientε with cancer, healthy donorε, and donorε with non-malignant diseases. To test the activity and cancer specificity of the general cancer-asεociated SCM-recognition factor containing ultrafiltrateε, 0.75 ml aliquots of potentially SCM-responding lymphocytes (5 X 10° cells/ml in PBS) were incubated for 40 min at 37°C with the ultrafiltrateε. 0.075 ml of the ultrafiltrates was used for each assay. SCM measurementε were carried out as previously described in the article by L. Cercek and B. Cercek, "Application of the Phenomenon of Changes in the Structuredneεs of Cytoplasmic Matrix (SCM) in the Diagnoεiε of Malignant Diεorders: a Review," Euro . J. Cancer 13. 903-915 (1977) and in the prior patent application by B. Cercek and L. Cercek, Serial No. 867,079, filed May 27, 1986, and entitled "Method for Measuring Polarized Fluorescence Emissions." In the SCM assay, a decrease in the intracellular fluorescence polarization value (P value) of at least 10% was taken aε a poεitive response to the challenging ultrafiltrate. TABLE 7 CROSSREACTIVITY OF SCM ACTIVITY OF ULTRAFILTRATES OF EXAMPLE 11 leases Responding/Cases Tested for Lymphocyte Donor with Diagnosis of: Diagnosis of Donor Cβ- Ca- Ca- CB- CB- CB- Ca- Cβ- Non-Cancer Healthy of Ultrafiltrate Mouth Larynx Cervix Ovary Lung Brain Breast Colon Diseases Donors Ca-Lung -- 2/2 3/3 -- 5/5 3/3 3/3 Ca-Bronchus 1/1 1/1 2/2 2/2 2/2 -- 2/2 Ca-Breast 1/1 1/1 3/3 2/2 2/2 — 3/3 Ca-Ovary 1/1 2/2 2/2 3/3 2/2 -- 2/2 Ca-Cervix 1/1 1/1 5/5 1/1 2/2 — 2/2 Ca-Colon 2/2 -- 3/3 -- 2/2 — 2/2 Ca-Houth 2/2 -- 1/1 — 1/1 — 1/1 Ca-Larynx 1/1 6/6 3/3 -- 2/2 — 2/2 Malignant Melanoma -- — -- -- -- -- 1/1 Glioblastoma -- -- 2/2 -- - 2/2 2/2 Appendicitis -- — — — 0/1 -- 0/1 Urethritis — — 0/2 -- 0/2 -- 0/1 Infectious Abscess -- 0/1 0/1 -- -- -- 0/1 Colitis — — 0/1 0/1 Sϋa PitUitβry 02 02 °/ 2 Healthy Donors -- — 0/2 0/1 0/3 -- 0/3 As the data of Table 7 show, potentially SCM- responding lymphocytes from patientε with eight different cancer typeε reεponded to ultrafiltrateε containing general cancer-associated SCM-recognition factors from nine different cancer types. In contrast, ultrafiltrateε from plaεmaε of healthy donors and donors with non-cancer diseases did not trigger any positive SCM responses. Also, neither did the potentially SCM-responding lymphocytes from healthy donors or thoεe with non- malignant conditions respond to any of the ultrafiltrates in the SCM test. Example 12 Modification of the SCM Response bv the Isolated SCM Factor To demonstrate the modification of the SCM response of lymphocytes free of malignancy by incubation with the isolated SCM factor, potentially SCM-responding lymphocytes were isolated from the blood samples of healthy donors and suεpended in complete Dulbecco's phosphate buffered saline (PBS) at 5 X 10 5 cells/ml as described in the European Journal of Cancer article, supra. and also in the prior patent application by B. Cercek, Serial No. 838,264, filed March 10, 1986, and entitled "Automated Collection of Buoyant Density Specific Cells from Density Gradients." Aliquots of these cells were incubated in 3 ml of the following: (a) cell-free blood plasma from cancer patientε; (b) plaεma from cancer patientε ultrafiltered for 12 hourε through an Amicon™ UM2 filter with a molecular weight cutoff of 1000 daltons; (c) plasma from cancer patients ultrafiltered for 12 hours through an Amicon™ UM5 filter with a nominal molecular weight cutoff of 500 daltons; (d) general cancer-aεsociated SCM factor as purified through the deεalting or Sephadex G-10 column stage; (e) the factor as purified through the Sephadex G-50 column stage; (f) the factor as purified through the DEAE- cellulose column step; (g) the factor as finally purified through the RP-HPLC step; and (h) plasma from healthy donorε ultrafiltered through an Amicon™ UM2 filter with a nominal molecular weight cutoff of 1000 daltonε. Theεe incubationε were performed for 2.5 hr. The ability of the SCM factor to modify the SCM reεponεe of the lymphocyteε from healthy donorε waε demonstrated by determining the SCM response ratio (R s CH ) of the lymphocyteε before and after the incubation with each of the fractionε deεcribed above. Before being contacted with either a mitogen or with the SCM factor for determination of the RR j ^ the incubated cellε were thoroughly waεhed. The preεence or abεence of modification was determined by the ratio of the polarization value of the lymphocyte suεpension after a short contact period with substrates containing the SCM factor over the polarization value of the lymphocyte suspenεion after a εhort contact period with phytohaemagglutinin (PHA) . In accordance with the SCM test procedure, a R s CH of lesε than 1.0 iε a poεitive indication of the preεence of malignancy in the donor while an P ^ of 1.1 or greater indicates the absence of malignancy. TABLE 8 MODULATION OF SCM RESPONSES OF LYMPHOCYTES FROM HEALTHY DONORS BY SCM FACTOR (EXAMPLE 12) ^CM 1 SCM Preparation Used For Before After Modulation ModulationModulation Cell-free Cancer Blood Plasma Ultrafiltrate of Cancer Blood Plasma (1000 Daltons Cutoff) Sephadex G-10 (SCM-Active) Sephadex G-50 (SCM-Active) DEAE-Cellulose (SCM-Active) RP-HPLC (SCM-Active) Ultrafiltrate of Cancer Blood Plaεma (500 Daltonε Cutoff) 1.38 1.38 Ultrafiltrate from Autologouε and Allogenic Blood Plaεma 1.38 1.38 from Healthy Donorε Table 8 indicateε the effect of the incubation with SCM-factor-containing fractionε on the response of the lymphocytes to either SCM factor or phytohaemagglutinin, as reflected in the Rs^. Lymphocytes which were either not preincubated, or which were preincubated with ultrafiltrate from healthy donors filtered through a filter with a nominal 1000-dalton molecular weight cutoff, or which were preincubated with ultrafiltrate from donors with cancer filtered through a filter with a nominal 500-dalton molecular weight cutoff, εhowed an PR^ of 1.35 or higher, aε expected. By contraεt, lymphocytes which were preincubated with fractions containing SCM factor all showed decreases in the R g a, to a value of 0.65-0.80 characteristic of lymphocytes originally isolated from patientε with malignant disease. Example 13 Effect of the Isolated SCM Factor on Lymphocyte Cytotoxicity To demonstrate the effect of the isolated SCM factor on the natural cytotoxicity of potentially SCM- responding lymphocytes toward malignant cells, such lymphocytes obtained from healthy donors were incubated for 2% hr at 37°C with plasma containing SCM factor isolated as previously described from blood samples of donors afflicted with cancer. Aliquots of theεe lymphocyteε were also retained as controls and not incubated. In addition, potentially SCM-responding lymphocytes were obtained from donors having cancer, and treated in the same manner—some aliquotε incubated with plasma containing SCM factor and others retained as controls and not incubated. After incubation the cytotoxicity of the lymphocytes waε teεted in accordance with the method deεcribed in M.R. Potter and M. Moore, "Natural Cytotoxic Reactivity of Human Lymphocyte Subpopulationε," Immunology 37. 187-194 (1979) . In accordance with thiε _ published method cells of the K 562 human myeloid cell line labeled with 51 Cr were used as target cells for the assay. The potentially SCM-responding lymphocytes were used as the effector cellε. The ratio of target cellε to effector cellε waε 1 to 20. Releaεe of the 51 Cr indicateε that the effector cellε are toxic to the target cell. The percent of cytotoxicity iε determined aε followε: R — R Percent cytotoxicity = — § — X 100 R τ - R c where R g is the percent of 51 Cr release in the sample, R c the percent of 51 Cr release in the control and R τ is the percent of 51 Cr release in the presence of a detergent, Triton X-100. The resultε are shown in Table 9. Theεe results show that incubation of potentially SCM- responding lymphocytes from healthy donors for 2.5 hr with ultrafiltrates filtered through filter with a nominal 1000-dalton molecular weight cutoff decreased their cytotoxicity by over 90%. When the incubation was performed with potentially SCM-responding lymphocyteε from cancer patients, the decreaεe in cytotoxicity waε smaller, between 40 and 90%. However, such lymphocytes from cancer patientε had lower levels of cytotoxicity before incubation, and the residual level of cytotoxicity remaining after incubation with ultrafiltrate was comparable to that remaining after incubation of lymphocytes from healthy donors. The lower level of cytotoxicity present in cells from cancer patients was consiεtent with a decrease of such cytotoxicity caused by in vivo exposure to factors such as the cancer-associated SCM recognition factor. TABLE 9 EFFECT OF SCM FACTOR ON NATURAL LYMPHOCYTE TOXICITY AGAINST K 562 HUMAN MYELOID CELL LINE (EXAMPLE 13) Example 14 Amino Acid Sequences of Isolated SCM Factors The amino acid sequences of isolated SCM factors, determined from purified preparations from blood plasmas of 12 different cancers, are preεented in Table 10. The εequenceε were determined by an automated Edman degradation procedure, uεing the Applied Bioεyεtemε 477A protein εequencer coupled with an online 120A PTH-amino acid analyzer. Sequence-calling software waε uεed to establish the amino acid residue at each cycle. The sequences of the SCM-factor peptides were obtained in repetitive analyses of two to three different preparations, isolated and purified to homogeneity, from pooled blood plasmas of about 5 to 50 different patients with a diagnosis of the same type of cancer. Amino acid residues designated in brackets below the primary, most significant residue detected at the particular degradation cycle represent εecondary amino acid residues present in some of the degradation cycles in significant amounts. These secondary residueε may indicate the presence of genetic polymorphisms of the SCM factors from individual blood donors contained in the sample pool that waε uεed for sequencing; many, but not all, of the subεtitutions in these polymorphiεms are conservative subεtitutions. In two caseε, where a total of 35 amino acidε were εeen, the last six were weak. This indicates that two separate factors were present in the preparations, one of 29 amino acidε, and a εecond of up to 35 amino acids. These two preparations were from donors with cancer of the prostate and seminoma of the testes. In some cases, no amino acid was seen in a particular cycle, designated by "X." These amino acids are moεt likely cysteine, and are otherwise referred to as cysteine (C) . This is because of the 20 common amino acids, cysteine is the only one not detectable by the Edman degradation procedure. TABLE 10 AMINO ACID SEQUENCES OF PURIFIED ISOLATED SCM FACTORS 10 20 30 Ca-BREAST: V I P P E V K F K K P F V F L M I D Q N T K T P L F M G K (M) (V) Ca-LUNG: M I P P E VK F M K P F V F L M I D Q N T K V P L F M G K (T) Ca-COLON: M I P P E V K F N t- P F V F L M I D Q N T K V P L F M G - (D) MELANOMA: M I P P E V I F N K P F V F L M I D Q N T K X P X F M G X SCC-CERVIX: M I P P E V K F N K P F V F L M I D Q N T K V P L F M G IC <S) Ca-OVARY: M I P P E V K F N KP F V F L M I D O N T i X X L F M GK (V) Ca-UTERUS: R I P P E V K F N K P F V F L M I D Q N T .. R P L F M G K (S) Ca-PANCREAS: V I P P E V K F N K P F V F L H I D Q N T K X P L F M G K Ca-RENAL: V I P P E V K F N X P F V F L M I D Q N T K V P L F M G IC Ca-GASTRIC: R I P P E VK F N K P F V F L M I D Q N T K X P X F M G X (V V N X T E) (SARCOMA) (S) U Ca-PROSTATE: V I P P E V K F N K P F V F L M I E O N T K S P L F M G K (V V N P T O) <S) W Ca-TESTIS: S I P P E VK F N KP F V F L M I E Q N T K S P L F M G K VV N P T Q (SEMINOMA) (V) Example 15 SCM Activity of Synthetic SCM Factor A synthetic SCM factor, representing the "consenεuε εequence" of M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-L- I-D-Q-N-T-K-V-P-L-F-M-G-K, waε εyntheεized using conventional solid-phaεe peptide synthesis techniques. Such techniques are described, for example, in M. Bodanszky, "Peptide Chemiεtry" (Springer-Verlag, Berlin, 1988), Ch. 10, "Solid Phase Peptide Synthesiε." The SCM activity of this synthetic SCM factor was tested by the standard SCM teεt. The fraction of SCM-reεponding lymphocyteε from patientε with a number of typeε of cancer and from normal healthy donors was challenged with the synthetic SCM factor. The factor was disεolved in εterile water for injectionε and was administered to the SCM-responding lymphocytes at 190 picomoles per 3 X 10 6 lymphocytes. As can be seen in Table 11, lymphocytes from patients with several types of cancer responded with significant decreases in intracellular fluorescein fluorescence polarization to the synthetic SCM factor. Most of these decreaseε in fluoreεcence polarization exceeded 40% and were comparable to the decreaεeε εeen with the moεt highly purified preparations of SCM factor isolated from blood plasma. This reεponse was also specific for lymphocytes from patientε with cancer. When lymphocytes from healthy donors were challenged with synthetic SCM factor, no decrease in fluorescence polarization was εeen, even when the cells were challenged with increased quantities of SCM factor as high as 960 picomoles per 3 X 10° lymphocytes. Example 16 Fragments of Synthetic SCM Factor Peptides representing distinct fragments of the synthetic SCM factor of Example 15 were syntheεized by conventional εolid-phase peptide synthesiε techniqueε. These peptides were designated F1-F5 and have the following sequences: Fl: M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-D-Q-N-T-K; F2: F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K; F3: F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K; F4: F-L-M-I-D-Q-N-T-K; and F5: M-I-P-P-E-V-K-F-N-K-P-F-V-F. These fragments represented the following portions of the complete εynthetic SCM molecule: Fl, amino acidε 1-22; F2, amino acidε 8-29; F3, amino acidε 8-22; F4, amino acidε 14-22; and F5, amino acidε 1-13. Example 17 Activity of Fragments of Synthetic SCM Factor of Example 16 in the SCM Test Fragments Fl through F5, representing different portions of the synthetic SCM molecule, were used as the challenging agents for both lymphocytes from patients with cancer and lymphocytes from normal donors in SCM teεts. The SCM tests were performed as described in Example 15. The results are shown in Table 11. Fragments Fl, F2, F3, and F4 were all fully active in the SCM test, while fragment F5 was inactive. For fragments Fl through F4, the expected specificity of the SCM responεe was maintained, as these fragments gave no decrease in fluorescence polarization when used to challenge lymphocytes isolated from donors free of malignancy. Of these peptides representing active fragmentε of the εynthetic SCM molecule, the smallest is F4, residues 14-22. All of the other active peptides include this segment, while F5, which does not have this εegment, iε inactive. Accordingly, reεidueε 14-22 can be conεidered to be the active site of the synthetic SCM- factor molecule. Significantly, this region of the peptide iε virtually invariant in the isolated SCM factors, except for the extremely conservative substitution of glutamic acid (E) for aspartic acid (D) at position 18 in two of the factors. - - TABLE 11 SCM ACTIVITY OF SYNTHETIC SCM FACTOR AND FRAGMENTS Fl TO F5 SCM Response as X of Control P Value to: Diagnosis of Synthetic Lymphocyte Donor SCM Factor F1 F2 F3 F4 F5 Melanoma Ca-Ovary Ca-Breast Melanoma Ca-Breast Ca-Breast Ca-Liver Ca-Stomach Ca-Testis Ca-Lung 99.5 Ca-Lung Ca-Breast 99.0 Healthy CM,30) Healthy (F,29) Healthy (M,36) Healthy (F,59) Healthy (M,28) Concentrations of synthetic SCM factor and fragments F1 to F5 used in these examples were 190 picomoles per 2 10° lymphocytes. Fragments represent the following amino acid residues of synthetic SCH factor: F1 (1-22); F2 (8-29); F3 (8-22); F4 (14-22); and F5 (1-13). P value denotes intracellular fluorescein fluorescence polarization value as measured with the SCM test. Example 18 Amphipathicity Profiles of SCM-active Peptides and Peptide Fragments Figure 1 shows the amphipathicity profile of the F4 peptide fragment. For comparison, Figure 2 also shows the amphipathicity profile of the synthetic SCM- active octapeptide whose sequence and SCM activity are disclosed in our co-pending patent application Serial No. 07/163,250, filed March 2, 1988, entitled "Synthetic SCM- Active Cancer Recognition Peptideε," and incorporated herein by thiε reference. The amphipathicity profiles of the SCM-active octapeptide and of F4 were nearly identical, even though only 4 of 8 of the amino acids of the octapeptide are homologous with thoεe of F4. Table 12 shows hydrophilicity values of the individual amino acids in the sequence of F4, the synthetic SCM-active octapeptide of our co-pending patent application Serial No. 07/163,250, and of the purified experimental allergic encephalitogenic (EAE) nanopeptide, which is inactive in the SCM test. The only difference between the synthetic SCM-active octapeptide and the inactive EAE nanopeptide is an additional serine residue in position 2. Serine haε a positive hydrophilicity value (+0.3), while in the active F4 fragment the first four residueε all have negative hydrophilicity valueε and in the εynthetic SCM-active octapeptide, residues 1, 2, and 4 have negative hydrophilicity values and residue 3, glycine, has a hydrophilicity value of 0.0. The hydrophilic serine in position 3 of EAE disrupts the sequence of negative hydrophilicities. Thiε disruption appears sufficient to prevent the recognition of EAE peptide by the receptorε i -'he lymphocyteε of cancer patientε that recognize the -sCM-active peptide. Accordingly, pure EAE peptide purified away from the SCM- active octapeptide is completely devoid of SCM activity. This example suggests the importance of amphipathicity profiles in controlling the recognition of the SCM factor by its corresponding receptor. TABLE 12 HYDROPHILICITY VALUES (HV) OF AMINO ACID (AA) SEQUENCES OF SCM-ACTIVE AND SCM-INACTIVE PEPTIDES I _ Example 19 Induction of SCM Response Characteristic of Malignancy in Lymphocytes from Healthy Donors bv Synthetic SCM Factor The synthetic SCM factor can induce an SCM responεe characteriεtic of malignancy in lymphocyteε from healthy donorε. The induction of thiε reεponεe requires active protein synthesis. To demonstrate thiε induction, SCM-reεponding lymphocytes from normal, healthy donors were isolated and divided into four aliquotε containing 5 X 10° cells/ml. Lymphocytes in the firεt aliquot were εuεpended in PBS and were used as untreated controls. Lymphocytes in the second aliquot were incubated with 400 picomoleε of εynthetic SCM factor, or, alternatively, with purified SCM factor from plaεma from patients with cancer. Lymphocytes in the third aliquot were incubated with 400 picomoleε of εynthetic SCM factor pluε 10 μg/ml of cycloheximide. Lymphocyteε in the fourth aliquot were incubated with 400 picomoles of synthetic SCM factor plus 10 μg/ml of actinomycin D. All four aliquots were incubated at 37°C for 2.5 hours. The aliquots were then washed three times with PBS, collected by centrifugation, and resuspended in PBS. The aliquots were then challenged with 190 picomoles of synthetic SCM factor per 2 X 10° cells for 40 min at 37°C and the intracellular fluorescein fluorescence polarization was determined for each sample as previouεly described. As can be seen in Table 13, untreated control lymphocytes from a healthy donor did not respond to synthetic SCM factor in the SCM test; i.e., there was no decrease in fluorescence polarization in compariεon to unchallenged control lymphocytes. In contrast, lymphocytes primed or induced by pretreatment with synthetic SCM factor responded with a significant decrease in fluorescence polarization when challenged either with εynthetic SCM factor or with purified SCM factor iεolated from blood plaεma of patients with colon cancer. This response was prevented when the pre-incubation occurred in the presence of the protein synthesiε inhibitors cycloheximide or actinomycin D, thus indicating that active protein synthesis was need to induce the response to SCM-active peptides. TABLE 13 IN VITRO INDUCTION OF SCM RESPONSES IN NORMAL, HEALTHY LYMPHOCYTES (NHL) BY PRETREATMENT WITH SYNTHETIC SCM FACTOR Treatment of NHL Source of SCM Response: Before Challenge Challenging P Value as with SCM Factor SCM Factor % of Control Untreated NHL Control NHL + Synthetic SCM Factor (2.5 hr incubation); Washed NHL + Synthetic SCM Factor (2.5 hr incubation); Washed NHL + Synthetic SCM Factor + 10 μg/ml Cycloheximide (2.5 hr incubation) ; Washed NHL + Synthetic SCM Factor + 10 μg/ml Actinomycin D (2.5 hr incubation); Waεhed Example 20 Preparation of Antibodies to Synthetic SCM Factor The synthetic SCM factor molecule was used to immunize experimental animals. Both pure εynthetic SCM- factor molecules and SCM conjugated to the carrier keyhole limpet hemocyanin (KLH) via an added carboxy- terminal cysteine using N-succinyl bromoacetate as the crosε-linking agent. Theεe immunogens were used to immunize female New Zealand rabbits. Both immunogens were diluted for primary immunization to 1.0 mg/ml with sterile PBS, combined with an equal volume of Freund's complete adjuvant, and emulsified. For primary immunization, a total of 25 μg or 50 μg of either synthetic SCM factor or synthetic SCM factor conjugated with KLH (SCM-KLH) was injected into each rabbit; two rabbits were used for each dose range. The inoculate was administered at 0.2 ml into two legs intramuscularly and over a minimum of 12 dorsal εiteε εubcutaneouεly at 0.2 ml per εite. One month later, the firεt booεter injection waε administered. Synthetic SCM factor and SCM-KLH were each administered with an equal-volume mixture of Freund's complete and incomplete adjuvants and emulsified. The booster inoculateε were injected via intramuscular and subcutaneouε εites similar to those used for primary inoculations. Total doses of 25 μg or 50 μg of immunogen per rabbit were administered in the booster injections. Blood samples taken 10 weeks after primary immunization yielded antisera containing higher amounts of immunoglobulins (IgG) from thoεe animals injected with 50 μg of immunogen than from those animals injected with 25 μg of immunogen. Radial immunodiffusion tests, conducted as described in W. Becker, "Determination of Antisera Titres Uεing the Single Radial Immunodiffuεion Method," Immunochemistrv 6., 539 (1969), gave precipitation reactions against the unconjugated SCM factor and SCM factor conjugated to bovine serum albumin (BSA) . To εeparate the immunoglobulinε containing the desired antibodies from the antiεera, the immunoglobulinε were firεt precipitated with an equal volume of saturated ammonium sulphate. The precipitates were then dissolved in 0.9% NaCl. To remove ammonium sulphate, the antibody- containing solutionε were either dialyzed or ultrafiltered 10 times through an Amicon™ membrane filter with a 5000-dalton molecular weight cutoff. Antibodies were kept frozen at -40°C until use. Example 21 ELISA Assay for SCM Factor A double-antibody enzyme-linked competitive immunosorbent aεsay (ELISA) was developed for detection of SCM factor by the use of antibodies raiεed againεt SCM factor (Example 20) . The ELISA aεεay iε depicted schematically in Figure 3. In the first step, SCM factor is attached to a εolid phase such as plastic, typically by pasεive adεorption. In the εecond step, the sample to be asεayed, along with a limited quantity of the anti-SCM antibody, iε added. After a thorough washing, an excesε of the labeled εecond antibody, goat anti-rabbit IgG labeled with the enzyme alkaline phoεphataεe, iε then added in the third εtep. The substrate for alkaline phosphatase, β-nitrophenylphosphate, is then added, and the absorbance at 405 nm (A 405 ) is measured. In this asεay, any free SCM factor added at the second step competes with the SCM factor adsorbed to the solid phase. Only the solid-phase SCM to which the first and second antibodies are bound yieldε color. Therefore, the higher is the concentration of SCM factor in the test sample, the lower is the measured A 405 . This is typical of a competitive assay. Variations on this procedure have been employed to detect SCM molecules in cancer cells, supernatants of growth culture media, blood plasma preparationε from cancer patients, and purified extracts of SCM from various sources. Example 22 Activity of Anti-SCM Antibodies The activity of the antibodies of Example 20 raised against both unconjugated SCM factor and the KLH- SCM factor conjugate was determined by a variation of the ELISA aεεay of Example 21. Different dilutionε of the antibodies were used, and no sample representing free SCM was added to the assay. The resultε are shown in Figure 4 for the antiserum raiεed againεt unconjugated SCM factor, and in Figure 5 for the KLH-SCM factor conjugate. Aε can be seen, both antibody preparations were active againεt purified SCM factor. Example 23 Determination of SCM-Factor Levels and Ultrafiltrates of Blood Plasmas by ELISA Asεav The level of SCM factor was determined in a number of ultrafiltrateε of blood plaεmaε from both healthy donorε and cancer patientε. Ultrafiltrateε of blood plaεmaε from 12 cancer patientε and 12 normal, healthy donors were prepared by filtration through an Amicon™ YM2 membrane filter with a 1000-dalton molecular weight cutoff. The level of SCM factor was assayed immunochemically by the ELISA aεεay of Example 21. The results are shown in Table 14. The levels of SCM factor detected by the ELISA aεεay were in the nanogram range per milliliter of ultrafiltrate. In the ultrafiltrateε from donorε with cancer, they were from 4.8 to 25.5 ng/ml. In normal, healthy donorε, the levelε of SCM factor were either below the minimum detectable level or up to a maximum of 1.85 ng/ml. TABLE 14 LEVELS OF SCM FACTOR IN AMICON™ YM2 ULTRAFILTRATES OF BLOOD PLASMAS FROM CANCER PATIENTS AND NORMAL, HEALTHY DONORS AS DETECTED BY ANTI-SCM FACTOR ANTIBODIES IN COMPETITIVE ELISA ASSAYS B ND = none detected Example 24 NH 2 -terminal Amino Acid Sequences of SCM Factor Secreted from Human Cancer Cells in Culture The partial NH 2 -terminal amino acid sequences of SCM-factor molecules present in the supernatant of serum- free culture media in which human cancer cells were grown were determined. The cells used were MCF7 breast cancer cells and HCT80 colon cancer cells. The presumed SCM- factor moleculeε from the εupernatants were isolated and purified to homogeneity using the combined procedures of Examples 1, 3, and 5 as deεcribed above for the purification of SCM factor from blood plaεma of cancer patientε. The εequence analyεeε on 8-picomolar amountε of the factor iεolated from the εupernatant culture medium from human MCF7 breaεt cancer cellε identified the firεt 16 NH 2 -terminal reεidueε as: M-I-P-P-E-V-X-F-N-K-P-F-(V- I-F-M) . The last four residues gave a weak signal. With two relatively conservative substitutions, methionine for valine in position 1 and isoleucine for leucine in poεition 15, 15 out of 16 of the amino acidε of thiε εegment are identical with the majority εequence of the SCM factor iεolated from plasma of patients with breast cancer in Example 14. At position 1, methionine was alεo found in the purified preparation from blood plaεma aε a less-frequent alternative to valine. Similarly, 5-picomole amounts of purified SCM factor from the supernatant culture medium of the culture of HCT-80 colon cancer cells were sequenced. Six amino- terminal amino acidε were determined: M-I-P-P-X-V. Five out of εix of theεe amino acidε are identical to thoεe determined on the SCM preparation purified from blood plasma of patients with colon cancer. The amino acid in poεition 4, denoted aε X, could not be determined due to the weak εignal. Example 25 Reactivity of SCM Factor Secreted from Human Cancer Cells In Culture with Anti-SCM-factor Antibodies The SCM factors secreted from human cancer cells in culture whose amino acid sequenceε were preεented in Example 24 alεo reacted with the anti-SCM antibody of Example 20. A variation on the ELISA assay of Example 21 was used. In this version of the ELISA asεay, the aεsay was performed directly on the eluate from the RP-HPLC purification step that remained adsorbed to the Eppendorf™ collection tubes after loading of the bulk of the eluates onto the εequenator diεk. No other SCM factor was added, and there was no additional εample added to the assay. This version of the SCM ELISA assay is noncompetitive; the larger is the quantity of SCM factor adsorbed to the Eppendorf™ tubes, the higher is the measured A 405 . The results, shown in Table 15, clearly indicate the presence of material able to react with anti-SCM antibody in theεe fractionε. TABLE 15 ELISA ASSAYS ON SCM FACTOR IN RP-HPLC ELUATES PURIFIED FROM CULTURE MEDIA OF CANCER CELLS Origin of Eluate MCF7 Breaεt Cancer Cellε MCF7 Breaεt Cancer Cellε MCF7 Breaεt Cancer Cellε HCT80 Colon Cancer Cellε HCT80 Colon Cancer Cellε "Background iε ELISA A A05 in tubeε without adεorbed SCM factor. Example 26 Detection of SCM Factor in Human Cancer Cells In Culture bv ELISA Assay Human cancer cells in culture were directly shown to contain SCM-factor molecules by antibody reactivity. Washed cellε from monolayered cultureε of εeveral human cancer cells: MCF7 breast cancer cellε; T1080 fibrosarcoma cells; A2780 ovarian cancer cellε; and HCT80 colon cancer cellε, were aεεayed directly by the noncompetitive ELISA aεεay procedure of Example 25. The data iε preεented in Table 16. The calculated ELISA abεorbance ratioε (i.e., the abεorbance in the presence of anti-SCM antibody divided by the absorbance in the absence of anti-SCM antibody, which are a relative measure of the amounts of SCM factor per 4 X 10 6 cells) εhowed that different cancer cell lineε produced, under identical conditionε, different amountε of SCM factor. Treatment of cultured cancer cellε with the protein synthesis inhibitor cycloheximide indicated that inhibition of protein synthesiε decreaεed the concentration of SCM factor aεεociated with the cultured cancer cells. The decrease was 25.3% for MCF7 breast cancer cells and 34% for T1080 fibrosarcoma cells. This data is preεented in Table 17. TABLE 16 SCM FACTOR IN HUMAN CANCER CELLS IN CULTURE AS DETECTED BY ELISA ASSAYS USING ANTI-SCM FACTOR ANTIBODY Human Cancer Cell Line (4 X 10 6 cells) ELISA A 405 Ratio 8 MCF7 Breast Cancer Cells 6.0 MCF7 Breast Cancer Cells 10.0 MCF7 Breast Cancer Cells 7.0 T1080 Fibrosarcoma Cells 6.5 A2780 Ovary Cancer Cells 4.6 HCT80 Colon Cancer Cells 3.0 ELISA A, 05 (cells + antibody) a ELISA A 405 Ratio = ELISA A, 05 (cells - antibody) _ _ TABLE 17 EFFECT OF CYCLOHEXIMIDE ON SCM FACTOR SYNTHESIS IN HUMAN CANCER CELLS IN CULTURE AS DETECTED BY ELISA ASSAYS USING ANTI-SCM FACTOR ANTIBODY 'Corrected k_ USB = (ELISA A^ in presence of cel ls) - (ELISA A«<, B in absence of cel ls) Example 27 Effect of SCM Factor on DNA Synthesis The effect of SCM factor on DNA εyntheεiε waε εtudied on normal rat hepatocyteε grown in culture. Detailε of the procedure were aε deεcribed in I. Hayashi & B.I. Carr, "DNA Synthesiε in Rat Hepatocyteε: Inhibition by a Platelet Factor and Stimulation by an Endogenous Factor," J. Cell. Phvsiol. 125. 82 (1985). Briefly, hepatocytes were obtained by the high-preεεure collagenase perfusion technique from male rat liverε. The cellε were plated at 3 X 10 5 cellε per 35-mm tiεεue cultured diεh in Dulbecco's modified Eagle's growth medium (DME) supplemented with 10% calf serum. Three hours after plating the cellε, the medium waε changed to serum-free DME to which 10 ng/ml of epidermal growth factor (EGF) was added to trigger DNA syntheεiε. To aliquots of the cell suεpenεion, SCM factor waε added in concentrations of 1000 ng/ml, 100 ng/ml, 10 ng/ml, 1.0 ng/ml, and 0.1 ng/ml. The culture medium was changed daily and the culture plateε were kept at 37°C in 5% C0 2 - air atmoεphere. About 72 hourε after plating, 5 μCi/ml of tritiated thymidine waε added to each diεh for about 6 to 8 hours. DNA synthesis was measured on cellε scraped off the tisεue plates with rubber policemen into glass tubes and collected by centrifugation. After waεhing once with PBS, 2 ml of cold 10% trichloroacetic acid (TCA) waε added to each tube and the cellε were kept at 4°C for one hour. After an additional waεh with 10% TCA, the cellε were collected by centrifugation and hydrolyzed in 1 ml of 0.5 N NaOH at 37°C overnight. Aliquotε of theεe samples were used for protein asεay uεing colorimetric measurement at 595 nm after staining with the protein- specific dye Coomassie brilliant blue. The remainder of the samples were used for measurement of tritiated thymidine incorporation. For thiε, sampleε were precipitated by addition of 0.25 ml of 50% TCA; after 10 minuteε on ice, they were passed through Whatman GF/C _ _ filters and dried. The uptake of tritiated thymidine into acid-precipitable material was counted in a Beckman scintillation counter. The resultε are preεented aε countε per minute incorporated per milligram of cellular protein in Table 18. The dose effect was highest at the lowest dose of the SCM factor, i.e., at 0.1 ng/ml, and decreased at higher doseε to a slight inhibition of DNA syntheεiε (13 percent) at 1000 ng/ml. Since the enhancement effect of SCM factor on DNA εyntheεiε waε assayed in this system in addition to the effect of EGF as a promoter of cell growth and DNA synthesis, the inhibitory effect at the highest dose of the SCM factor could be the reaction to exceεεive εtimulation in the presence of both the SCM factor and EGF. TABLE 18 EFFECT OF SCM FACTOR ON DNA SYNTHESIS OF RAT HEPATOCYTES SCM Factor Doεe Relative DNA Synthesis (ng/ml) Per μg DNA (%) a 1000 86.5 100 134.5 10 171.5 1 184.0 0.1 192.4 a Relative DNA syntheεiε per μg DNA = cpm/μg DNA (EGF + SCM Factor) - cpm/μg DNA (EGF only) cpm/μg DNA (EGF) - cpm (Background) Data waε corrected for quenching cauεed by varying protein content. Example 28 Effect of SCM Factor on Inhibition of Serine Proteases bv Q.-1-PI Protease Inhibitor A protease activity using caεein-reεorufin aε a protease substrate was performed to determine the effect of SCM factor on inhibition of the serine proteaseε trypsin, elastase, and cathepsin G by the serine protease inhibitor α-l-PI. The protocol provided by the manufacturer, Boehringer-Mannheim Biochemica, was followed to aεεay proteaεe activity. Table 19 shows the resultε when trypεin was used, Table 20 shows the results when elastaεe waε used, and Table 21 εhowε the reεultε when cathepεin G waε uεed. In each caεe, SCM factor by itεelf did not affect the proteolytic activity. However, when SCM factor waε added before α-l-PI or εimultaneouεly in a mixture with α-l-PI, it prevented the inhibition of trypεin by α-l-PI. The degree of thiε effect depended on the quantity of SCM factor added. In contraεt, aε can be seen in Table 19, when α-l-PI was allowed to react first with trypsin, subεequent addition of SCM factor did not reverεe the inhibition of trypεin by α-l-PI. The active portion of the molecule that preventε inhibition of the proteolytic enzymeε by α-l-PI reεideε within the firεt εeven amino-terminal amino acid reεidueε of the SCM factor. This portion of the molecule is designated "fraction 6" or F6. The effectiveneεε of equimolar amountε of the peptide F6, aε compared to the entire SCM factor molecule (Table 20) in preventing the inhibition of elaεtaεe by α-l-PI is shown in Table 22. TABLE 19 EFFECT OF SCM FACTOR ON INHIBITION OF TRYPSIN ACTIVITY BY α-l-PI PROTEASE INHIBITOR Trypsin Activity in Casein-Reεorufin Aεεay aε % of Sequence of Addition Untreated of Reaction Components 8 Control Enzyme 3 μg Trypεin (control) 100.0 3 μg Trypεin + 230 μg SCM Factor 99.9 3 μg Trypεin + 6.6 μg α-l-PI 13.6 3 μg Trypsin + 6.6 μg α-l-PI (60 min inc.) + 230 μg SCM Factor 14.0 3 μg Trypsin + 21 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 15.6 3 μg Trypsin + 60 μg SCM Factor (10 min inc.) + 6.6 μg cc-l-PI 40.0 3 μg Trypεin + 100 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 62.5 3 μg Trypεin + 150 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 97.7 3 μg Trypεin + 230 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 101.7 6.6 μg 0.-1-PI + 230 μg SCM Factor (10 min inc.) + 3 μg Trypsin 100.6 a Total reaction volume is 300 μL. TABLE 20 EFFECT OF SCM FACTOR ON INHIBITION OF ELASTASE ACTIVITY BY α-l-PI PROTEASE INHIBITOR Trypsin Activity in Casein-Resorufin Aεsay as % of Sequence of Addition Untreated of Reaction Components 8 Control Enzyme 3.2 μg Elastase (control) 100 . 0 3.2 μg Elastase + 230 μg SCM Factor 100. 0 3.2 μg Elastase + 6.6 μg α-l-PI 3 . 5 3.2 μg Elastase + 10 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 6 . 4 3.2 μg Elastase + 30 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 7 . 0 3.2 μg Elastase + 60 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 55.8 3.2 μg Elastase + 100 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 71. 1 3.2 μg Elastase + 150 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 77 .5 3.2 μg Elastase + 230 μg SCM Factor (10 min inc.) + 6.6 μg α-l-PI 90 . 1 a Total reaction volume is 300 μL. TABLE 21 EFFECT OF SCM FACTOR ON INHIBITION OF CATHEPSIN G ACTIVITY BY α-l-PI PROTEASE INHIBITOR Cathepsin G Activity in Caεein- Reεorufin Aεεay aε Sequence of Addition of % of Untreated Reaction Components 8 Control Enzyme 1 μg Cathepεin G (control) 100.0 1 μg Cathepsin G + 240 μg SCM 97.0 Factor 1 μg Cathepsin G + 6.6 μg α-l-PI 20.0 1 μg Cathepsin G + 240 μg SCM Factor (10 min inc.) + 6.6 μg α- 103.0 1-PI a Total reaction volume is 300 μL. TABLE 22 EFFECT OF AMINO-TERMINAL PEPTIDE FRAGMENT F6 (AMINO ACIDS 1-7) OF SCM FACTOR ON INHIBITION OF ELASTASE ACTIVITY BY α-l-PI PROTEASE INHIBITOR Elastase Activity in Casein-Reεorufin Aεsay as % of Sequence of Addition of Untreated Control Reaction Componentε 8 Enzyme 3.2 μg Elastase (control) 100. 0 3.2 μg Elastaεe + 120 μg F6 98. 0 3.2 μg Elaεtaεe + 6.6 μg α-l-PI 3 .4 3.2 μg Elaεtaεe + 7.2 μg F6 (10 min inc.) + 6.6 μg α-l-PI 3 . 8 3.2 μg Elaεtaεe + 21.6 μg F6 (10 min. inc.) + 6.6 μg o.-1-PI 9 . 8 3.2 μg Elaεtaεe + 30.0 μg F6 (10 min inc.) + 6.6 μg α-l-PI 34 .2 3.2 μg Elaεtaεe + 60.0 μg F6 (10 min inc.) + 6.6 μg α-l-PI 38. 0 3.2 μg Elastase + 120.0 μg F6 (10 min inc.) + 6.6 μg α-l-PI 96. 3 a Total reaction volume is 300 μL. Example 29 Interaction of Protease Inhibitor α-l-PI With SCM-Factor Receptors The protease inhibitor α-l-PI waε εhown to interact εtrongly with SCM-factor receptors on SCM- responding lymphocytes from cancer patientε. Thiε interaction waε εhown by the removal of the SCM-factor receptorε from εuch lymphocyteε by waεhing after incubation with α-l-PI. This caused reversion of the SCM response to that typical of lymphocytes from donors free of cancer. SCM-reεponding lymphocyteε were iεolated from blood εampleε of a patient with malignant melanoma and from a normal, healthy donor. Half of the lymphocyte εuεpension from each sample was incubated with 30 nanomoleε of α-l-PI per 6 X 10° cellε for 2.5 hourε at 37°C; the other half waε retained aε an untreated control. The cellε were then washed three times with PBS. Aliquotε from both the untreated controlε and the α-l-PI-treated εampleε were challenged for 40 min with phytohemagglutinin (PHA) or SCM factor. The SCM reεponses were meaεured by changes in intracellular fluorescein fluorescence polarization as described above under "Performance of the SCM Test." As can be εeen in Table 23, the control lymphocyteε from the melanoma patientε had a RR gp ,, of 0.63, a typical value for lymphocytes from donors with cancer. The same lymphocytes pre-incubated with α-l-PI had an PR^ of 1.8, a value typical of lymphocytes from healthy donorε. By contrast, incubation of lymphocytes from normal, healthy donors with ot-l-PI did not materially effect the responεeε of theεe cellε in the SCM teεt to PHA. The R g ,, waε 1.74 in the abεence of incubation and 1.68 after incubation. TABLE 23 SCM-RESPONSE MODIFYING EFFECT OF α-l-PI Example 30 Inhibition of SCM Factor Svnthesiε Aε shown in Table 17 of Example 26, treatment of human cultured cancer cells with cycloheximide, an inhibitor of protein syntheεiε, decreaεes the amount of SCM factor produced by these cells. Similarly, ascorbic acid waε εhown to inhibit the εyntheεis of SCM factor by MCF7 human breast cancer cells in culture. The amounts of SCM factor per 7 X 10° cells in the presence or absence of 10 "3 molar ascorbic acid after a 16-hour incubation were measured by the noncompetitive ELISA procedure of Example 25. The resultε are εhown in Table 24. The aliquot of cancer cellε incubated in the preεence of ascorbate ions produced 43.9% less SCM factor than untreated control cellε. The obεerved inhibition of SCM factor εynthesis by aεcorbic acid could be the reεult of decreaεed metabolic activity of treated cancer cells since ascorbic acid was εhown to εelectively induce in cancer cells the transition of mitochondria into the idling, orthodox conformation, as described in L. Cercek & B. Cercek, "Effects of Ascorbate Ions on Intracellular Fluorescein Emission Polarization Spectra in Cancer and Normal Proliferating Cells," Cancer Detection & Prevention 10. 1-20 (1987) . _ _ TABLE 24 EFFECT OF ASCORBATE IONS ON SCM FACTOR SYNTHESIS IN CULTURED MCF7 HUMAN BREAST CANCER CELLS Corrected Treatment During 16 hrε of Corrected ELISA A 405 as Incubation at 37°C ELISA A 405 a % of Control None (Control) 1.7448 100.0 X ID "3 M L-ascorbic acid, 0>g7gg 56 1 p-ti / .1 a Corrected ELISA A 405 = (ELISA A 405 ) - (Background A 405 ) Example 31 Effect of Synthetic SCM Factor and Fragments Thereof on Natural Cytotoxicity of Lymphocytes The purified synthetic SCM factor molecule and peptides F1-F5, F7, and F8, as described above in Example 16, were inveεtigated to determine their εuppreεεive effect on the natural cytotoxicity of lymphocyteε againεt cancer cellε, using the human myeloid cell line K 562 as target as measured by the conventional 51 Cr release method (Example 13) . In brief, the K 562 target cells grown in suspension in RPMI-FBS culture medium were washed and labeled for 3 hours at 37°C with 100 μCi εodium [ 51 Cr]chrornate and then waεhed 4 timeε in RPMI growth medium. The effector lymphocytes used were isolated from heparinized peripheral blood of normal healthy donors using either appropriate density solutions to isolate the SCM-responding subpopulation of lymphocyteε, as described above under "Iεolation of SCM-reεponding Lymphocyteε," or the conventional εeparation medium Histopaque 1077 for isolation of the total population of peripheral blood lymphocyteε (PBL) . The effector cell to target cell ratio uεed in theεe experimentε waε 40:1. Control samples contained target cells only and were used to determine background isotope release from the target cells. The test sampleε contained 0.2 mL aliquotε of labeled target cellε to which 0.2 mL of effector lymphocyteε waε added; the effector lymphocyteε were either untreated or had been pretreated with either the entire synthetic SCM factor or any of the fragments designated Fl to F5, F7, or F8 for 2.5 hours at 37°C. The teεtε were carrieε out in triplicate. Cell εuεpensions were incubated for 18 hourε at 37°C in an atmosphere of 95% air and 5% C0 2 . Samples were then centrifuged for 10 minuteε at 200 xg. From each teεt εample tube, a 0.2 mL aliquot of the supernatant was removed. Both the supernatant and the remaining cell pellet were counted in a Beckman gamma counter. The _ _ maximum possible isotope release was taken as the count obtained by adding the counts for the supernatant and cell pelletε. The percentage of 51 Cr releaεe waε determined for each of the triplicate samples; using the mean value of 51 Cr releaεe, the percentage of cytotoxicity was calculated according to the equation presented in Table 25. As shown in the experimentε whoεe reεultε are given in Table 25, incubation of SCM-reεponding lymphocyteε and of PBL with 35 femtomoles of synthetic SCM factor per lymphocyte decreased their natural killing efficiency or cytotoxicity against K 562 cells by 97% to 99.9% as compared to cytotoxicity of the untreated effector lymphocytes. This confirms the resultε previously obtained with the natural SCM factor preεent in ultrafiltrateε of blood plasma from patients with cancer. The synthetic SCM factor suppreεεeε the cytotoxicity of both the SCM-responding subpopulation of lymphocyteε and the entire PBL population. Aε εhown in Table 25, the NK-suppressive effect of synthetic SCM factor is irreversible and cannot be reversed by multiple washing of treated lymphocytes. TABLE 25 EFFECT OF SYNTHETIC SCM FACTOR ON NATURAL LYMPHOCYTE CYTOTOXICITY AGAINST K 562 MYELOID CELLS a All lymphocytes were isolated from normal healthy donors. SCM-R is the subpopulation of peripheral blood lymphocyteε isolated from density gradient solutions, that yield the subpopulation which respondε to phytohaemagglutinin (PHA) in the SCM teεt. PBL iε the total population of peripheral blood lymphocytes isolated on Histopaque 1077 denεity εolution. b Cytotoxicity was determined aε in Example 13. c Treated lymphocyteε were treated with 35 femtomoleε of synthetic SCM factor per lymphocyte. Values given are the mean of triplicate tests in each experiment. The effector/target ratio was 40:1. To establish which part of the SCM-factor molecule is responsible for this NK-suppressive effect, we have treated the effector lymphocytes with peptides representing different regions of the amino acid εequence of εynthetic SCM factor. As shown in Table 26, peptides that did not contain the seven carboxyl-terminal amino acids had no effect on the natural cytotoxicity of lymphocytes. However, peptides containing residueε 14-29 (fragment F2) or 23-29 (fragment F8) are alεo inactive in suppressing cytotoxicity. Therefore the NK-suppressive activity appears to require the presence of amino acid residueε 8-29 of the synthetic SCM molecule. This region is different from the region of synthetic SCM factor responsible for protection of protease from inhibition by α-l-PI, which resides in the amino terminus of the molecule (Example 28) . It is also more extensive than the region of the SCM molecule responεible for SCM activity (reεidueε 14-22), although it overlaps that region (Example 17). For example, peptide fragment F4, which extends from residue 14 to residue 22 and is fully active in the SCM test, does not cause any suppression of NK activity. TABLE 26 DETERMINATION OF THE CYTOTOXICITY SUPPRESSIVE PORTION OF THE SYNTHETIC SCM MOLECULE Percent Cytotoxicity": Synthetic Control SCM Factor Untreated (1-29)" 72.7 ± 1.23.2 ± 0.1 78.5 ± 1.014.9 ± 1.574.5 ± 1.576.2 ± 1.372.7 ± 1.3 80.4 ± 1.03.1 ± 0.881.0 ± 1.02.6 ± 1.780.5 ± 1.081.0 ± 1.579.8 ± 0.9 46.5 ± 1.5 0.1 ± 0.8 — 2.4 ± 0.2 — 48.6 ± 1.3 71.2 ± 1.5 72.7 ± 1.071.7 ± 1.2 31.0 ± 2.0 33.0 ± 1.8 "Percent cytotoxicity was determined as in Example 13 using PBL. Lymphocytes were incubated with 35 femtomoles of either the entire synthetic SCM factor or peptides representing portions of it, for 2.5 hours at 37 β C. "The nunerals in parentheses indicate the numbers of the amino acid residues included in the particular fragment of synthetic SCM factor. Values given are the mean of triplicate tests in each experiment. The effector/target ratio was 40:1. - -i~ ADVANTAGES OF THE PRESENT INVENTION Both the iεolated and purified SCM factorε of the present invention and the synthetic SCM factorε and fragmentε of the preεent invention meet the needε previously enumerated. In particular, they allow the assay of the SCM responεe by the use of homogeneous challenging agents of defined structure. The availability of such challenging agentε eliminates the need to use challenging agents partially purified from tiεεue extractε in the SCM aεεay. Such partially purified challenging agentε are non-homogeneous, can vary from batch to batch in purity and potency, and can contain contaminants that interfere with the SCM test. The challenging agents of the present invention therefore give greater reliability and uniformity in both clinical and research studies. The knowledge of the complete amino acid sequences of such SCM factor molecules allows their synthesis in quantity by either solid-phase peptide synthesis techniques or, alternatively, by genetic engineering techniques that can expresε the peptideε in cellε containing recombinant DNA. Additionally, the availability of homogeneous and purified preparations of SCM factorε makeε poεεible the preparation of antibodies specific to them. The preparation of such antibodies allows the performance of immunoassays for the detection and monitoring of small quantities of SCM factor in vivo. This gives a new, noninvasive tool for the early detection of cancer and the monitoring of the efficacy of cancer treatment. Such assays can, for example, identify metastaεeε before they would be otherwiεe detectable. Such antibodies can also be used directly in treatment methods to reduce the effect of SCM factors in vivo and enhance the reεiεtance of cancer patientε to the disease. In addition to aεεays of clinical importance, the availability of such factors opens up new avenues for studying cancer. The ability to vary the amino acid sequenceε of the SCM factorε in known wayε allowε the performance of structure-activity studieε otherwiεe impossible. Also, the ability to label such factors allows the isolation of receptors or other molecules that interact with SCM factors in vivo. The pure, appropriately labeled SCM factor can be used for detection of receptorε for the SCM factor on patientε' lymphocyteε. Thiε can provide an alternative to the SCM teεt. Although the preεent invention haε been deεcribed in conεiderable detail with regard to certain preferred verεionε thereof, other verεions are posεible. Therefore, the εpirit and scope of the appended claims should not be limited to the descriptionε of the preferred verεions contained herein.

Claims: What is claimed is: 5. A substantially purified cancer recognition factor, the factor being a peptide of at least 9 amino acid reεidueε including a core sequence of 9 amino acid residueε having an amphipathicity profile substantially equivalent to that of the sequence F-L-M-I- D-Q-N-T-K, the factor producing at least a 10 percent decrease in the intracellular fluorescence polarization value of lymphocytes capable of reεponding in the εtructuredneεs of the cytoplasmic matrix (SCM) test isolated from donors afflicted with cancer. 6. The cancer recognition factor of claim 1 producing at least a 25 percent decrease in the intracellular fluorescence polarization value of SCM- responding lymphocyteε from donorε afflicted with cancer. 7. The cancer recognition factor of claim 1 wherein the core εequence of 9 amino acid residues is F- X 15 -M-X 17 -X 18 -X 19 -X 20 -X 2 -,-K, wherein X 15 and X 17 are each independently selected from the group consisting of I, L, and V; X 18 is selected from the group consisting of D and E; X 19 and X 20 are each independently selected from the group consisting of Q and N; and X 21 is selected from the group consiεting of S and T. 8. The cancer recognition factor of claim 3 wherein the core sequence of 9 amino acid residues is F- L-M-I-D-Q-N-T-K. 9. The cancer recognition factor of claim 1 wherein the peptide has the εequence F-X 15 -M-X 17 -X 18 -X 19 -X 20 - X^-K, wherein X 15 and X 17 are each independently selected from the group consisting of I, L, and V; X 18 is εelected from the group consisting of D and E; X 19 and X 20 are each independently selected from the group consiεting of Q and N; and X 21 is selected from the group consisting of S and T. 10. The cancer recognition factor of claim 5 wherein the peptide has the sequence F-L-M-I-D-Q-N-T-K. 11. The cancer recognition factor of claim 1 wherein the peptide has the sequence F-X 9 -K-P-F-X l3 -F-X 15 - M-X 17 -X 18 -X 19 -X 20 -X 21 -K, wherein X 13 , X 15 and X 17 are each independently selected from the group consisting of I, L, and V; X 18 is selected from the group consisting of D and E; ς ,, X 19 and X 20 are each independently selected from the group consisting of Q and N; and X 21 is selected from the group consisting of S and T. 12. The cancer recognition factor of claim 7 wherein the peptide has the sequence F-N-K-P-F-V-F-L-M-I- D-Q-N-T-K. 13. The cancer recognition factor of claim 1 wherein the peptide has the sequence F-X p -K-P-F-X^-F-X- jg - M-X^-X^-X^-X^-X^-K-X^-P-X^-F-M-G-K, wherein X 13 , X 15 , X 17 , X^, and X jg are each independently selected from the group consisting of I, L, and V; X 18 is εelected from the group consisting of D and E; X g , X 19 and X 20 are each independently selected from the group consiεting of Q and N; and X 21 iε εelected from the group consisting of S and T. 14. The cancer recognition factor of claim 9 wherein the peptide has the sequence F-N-K-P-F-V-F-L-M-I- D-Q-N-T-K-V-P-L-F-M-G-K. 15. The cancer recognition factor of claim 1 wherein the peptide has the sequence M-X 2 -P-P-X 5 -X 6 -K-F-X 9 - K-P-F-X 13 -F-X l5 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K, wherein X 2 , X 6 , X 13 , X 15 and X 17 are each independently selected from the group consisting of I, L, and V; X 5 and X 18 are each independently selected from the group consisting of D and E; X g , X 19 and X 20 are each independently selected from the group consisting of Q and N; and X 21 is εelected from the group consisting of S and T. 16. The cancer recognition factor of claim 11 wherein the peptide haε the εeguence M-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K. 17. A εubεtantially purified cancer recognition factor uεeful in the structuredness of the cytoplasmic matrix (SCM) test consiεting eεsentially of a peptide having an amino acid sequence of M-X 2 -P-P-X 5 -X 6 -K- F-X p -K-P-F-X^-F-X^-M-X^-X^-X^-X^-X^-K-X^-P-X^-F-M-G-K, wherein X 2 , X 6 , X 13 , X 15 , X 17 , X^, and X 25 are each independently selected from the group consisting of I, L, and V; X 5 and X 18 are each independently selected from the group conεiεting of D and E; X 9 , X 19 and X 20 are each independently εelected from the group conεisting of Q and N; and X 21 is εelected from the group consisting of S and T, the factor producing at least a 10 percent decrease in the intracellular fluoreεcence polarization value of SCM- responding lymphocytes from donors afflicted with cancer. 18. A substantially purified cancer recognition factor useful in the structuredness of the cytoplasmic matrix (SCM) teεt conεiεting essentially of a peptide of from 29 to 35 amino acid reεidues including a core sequence at amino acids 14 through 22 of F-L-M-I-X 18 - Q-N-T-K, wherein X 18 is εelected from the group conεiεting of D and E, the factor producing at least a 10 percent decrease in the intracellular fluorescence polarization value of SCM-responding lymphocytes from donors afflicted with cancer. 19. The factor of claim 14 wherein the peptide has the amino acid sequence X 1 -I-P-P-X 5 -V-K-F-N-K-P-F-V-F- L-M-I-D-Q-N-T-K-X^-P-L-F-M-G-K, wherein X, iε selected from the group consisting of V, M, and S; X 5 is selected from the group consiεting of E and D, and ^ iε εelected from the group conεisting of T and V. 20. The cancer recognition factor of claim 15 wherein the factor has the sequence V-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K. 21. The cancer recognition factor of claim 15 wherein the factor has the sequence M-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K. 22. The cancer recognition factor of claim 14 wherein the factor haε the εequence M-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-C-P-C-F-M-G-C. 23. The cancer recognition factor of claim 14 wherein the factor haε the εequence X.,-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-C-C-L-F-M-G-K, wherein X, iε selected from the group consiεting of M and V. 24. The cancer recognition factor of claim 19 wherein the f ctor haε the εequence M-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-C-C-L-F-M-G-K. 25. The cancer recognition factor of claim 14 wherein the factor has the sequence X^I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-R-P-L-F-M-G-K, wherein X 1 is selected from the group consiεting of R and S. 26. The cancer recognition factor of claim 21 wherein the factor haε the εequence R-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-R-P-L-F-M-G-K. 27. The cancer recognition factor of claim 14 wherein the factor has the sequence V-I-P-P-E-V-K-F-N-K- P-F-V-F-L-M-I-D-Q-N-T-K-C-P-L-F-M-G-K. 28. The cancer recognition factor of claim 14 wherein the factor has the sequence V-I-P-P-E-V-K-F-N-C- P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K. 29. The cancer recognition factor of claim 14 wherein the peptide is selected from the group consisting of peptides having amino acid sequences X.,-I-P-P-E-V-K-F- N-K-P-F-V-F-L-M-I-D-Q-N-T-K-C-P-C-F-M-G-C and X^I-P-P-E- V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-C-P-C-F-M-G-C-V-V-N-C- T-E, wherein X 1 is selected from the group consisting of R and S. 30. The cancer recognition factor of claim 25 wherein the peptide haε the amino acid sequence R-I-P-P- E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-C-P-C-F-M-G-C. 31. The cancer recognition factor of claim 14 wherein the peptide is selected from the group consisting of peptides having amino acid sequences X.,-I-P-P-E-V-K-F- N-K-P-F-V-F-L-M-I-E-Q-N-T-K-S-P-L-F-M-G-K and X^I-P-P-E- V-K-F-N-K-P-F-V-F-L-M-I-E-Q-N-T-K-S-P-L-F-M-G-K-V-V-N-P- T-Q, wherein X 1 is selected from the group conεiεting of V and S. 32. The cancer recognition factor of claim 27 wherein the peptide haε the amino acid sequence V-I-P-P- E-V-K-F-N-K-P-F-V-F-L-M-I-E-Q-N-T-K-S-P-L-F-M-G-K. 33. The cancer recognition factor of claim 14 wherein the peptide haε the amino acid sequence X.,-I-P-P- E-V-K-F-N-K-P-F-V-F-L-M-I-E-Q-N-T-K-S-P-L-F-M-G-K-V-V-N- P-T-Q, wherein X 1 is εelected from the group consisting of S and V. 34. The cancer recognition factor of claim 29 wherein the peptide has the amino acid sequence S-I-P-P- E-V-K-F-N-K-P-F-V-F-L-M-I-E-Q-N-T-K-S-P-L-F-M-G-K-V-V-N- P-T-Q. 35. A substantially pure cancer recognition factor active in the structurednesε of the cytoplaεmic matrix (SCM) teεt conεiεting essentially of low molecular weight peptide passing through filters with a nominal 1000-dalton molecular weight cutoff and retained by filters with a nominal 500-dalton molecular weight cutoff, the factor providing at least a ten percent decrease in the intracellular fluorescence polarization value of SCM-responding lymphocytes from donors afflicted with cancer as meaεured by the standard SCM test. 36. The cancer recognition factor of claim 31 producing at least a twenty-five percent decrease in the intracellular fluorescence polarization value of SCM- responding lymphocytes from donors afflicted with cancer as measured by the standard SCM test. 37. A method for testing lymphocytes obtained from a mammalian donor for the presence or absence of malignancy in the donor compriεing the εtepε of: (a) contacting a εuspension of the lymphocytes with the subεtantially purified cancer recognition factor of claim 1, 13, 14, or 31; and (b) determining the decreaεe in the structuredness of the cytoplasmic matrix of the lymphocytes resulting from the step of contacting the suspension of the lymphocytes. 38. The method of claim 33 wherein the step of determining the decrease in the structurednesε of the cytoplaεmic matrix compriεeε the εtepε of: (a) meaεuring the fluorescence polarization, P s , for a first aliquot of the lymphocyteε that has been contacted with the cancer recognition factor; (b) measuring the fluorescence polarization, P c , for a second aliquot of the lymphocytes that has not been contacted with the cancer recognition factor; and (c) determining the ratio of P s to P c , whereby a ratio of P s to P c of less than about 0.9 indicates the presence of a malignancy in the body of the donor of the lymphocytes. 39. The method of claim 33 wherein the step of determining the decrease in the structuredness of the cytoplasmic matrix compriseε the εtepε of: (a) measuring the fluorescence polarization, P s , for a first aliquot of the lymphocytes that has been contacted with the cancer recognition factor; (b) measuring the fluorescence polarization, P M , for a second aliquot of the lymphocytes that has been contacted with a mitogen selected from the group consisting of phytohaemagglutinin, concanavalin A, and pokeweed mitogen; and (c) determining an SCM responεe ratio, RR^, as the ratio of P s to P H , whereby an RR SCH of lesε than about 0.9 indicates the presence of a malignancy in the body of the donor of the lymphocytes. 40. A method for screening a blood sample for the presence of a malignancy in the body of the donor of the blood εample compriεing the εtepε of: (a) separating potentially SCM-responding lymphocyteε from the blood sample; (b) contacting the εeparated lymphocytes with the substantially purified cancer recognition factor of claim l, 13, 14, or 31 to stimulate the lymphocytes; (c) contacting the stimulated lymphocytes with a fluorogenic agent precursor for a sufficient time for the precursor to penetrate the lymphocytes for intracellular enzymatic hydrolysiε to a fluorogenic agent, thereby generating εtimulated fluorogenic agent- containing lymphocyteε; (d) exciting the εtimulated fluorogenic agent-containing lymphocyteε with polarized light thereby causing the lymphocytes to fluoresce; (e) meaεuring the vertically polarized and horizontally polarized fluorescence emissions from the fluorescing lymphocytes for determining a polarization value for the fluorescing lymphocyteε; and (f) comparing the determined polarization value for the stimulated lymphocytes with the polarization value for a control aliquot of lymphocytes from the same donor which has been εubjected to the operation of εteps (a) , (c) , (d) , and (e) , but not (b) , thereby to indicate the presence or absence of cancer in the body of the donor of the lymphocytes. 41. The method of claim 36 wherein stepε (b) and (c) occur εimultaneouεly. 42. An antibody εpecific for the εubstantially purified cancer recognition factor of claim 1, 13, 14, or 31. 43. The antibody of claim 38 which iε specific for a cancer recognition factor with an amino acid sequence of F-L-M-I-D-Q-N-T-K. 44. The antibody of claim 38 which is specific for a cancer recognition factor with an amino acid sequence of M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K- V-P-L-F-M-G-K. 45. A monoclonal antibody specific for the substantially purified cancer recognition factor of claim 1, 13, 14, or 31. 46. The monoclonal antibody of claim 41 which is specific for a cancer recognition factor with an amino acid sequence of F-L-M-I-D-Q-N-T-K. 47. The monoclonal antibody of claim 41 which is specific for a cancer recognition factor with an amino acid sequence of M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N- T-K-V-P-L-F-M-G- . 48. A method for determining the level of cancer recognition factor in a body fluid comprising the εtepε of: (a) mixing the body fluid and the antibody of claim 38; and (b) determining the extent of reaction between the cancer recognition factor in the body fluid and the antibody by performing an immunoaεsay. 49. The method of claim 43 wherein the immunoassay is selected from the group consisting of radioimmunoasεayε, fluoreεcence immunoassays, chemiluminescence immunoassays, enzyme-linked immunoasεayε, and immunoaεεayε dependent on aggregation of antigen-antibody complexeε. 50. A method for determining the level of cancer recognition factor in a body fluid comprising the steps of: (a) mixing the body fluid and the monoclonal antibody of claim 41; and (b) determining the extent of reaction between the cancer recognition factor in the body fluid and the monoclonal antibody by performing an immunoassay. 51. The method of claim 46 wherein the immunoassay is selected from the group consiεting of radioimmunoassays, fluoreεcence immunoassays, chemiluminescence immunoassays, enzyme-linked immunoassays, and immunoasεayε dependent on aggregation of antigen-antibody complexeε. 52. A recombinant DNA εequence encoding the εubstantially purified cancer recognition factor of claim 1, 13, or 14 in isolation from DNA encoding proteinε normally accompanying cancer recognition factor. 53. The DNA sequence of claim 48 encoding a cancer recognition factor with an amino acid sequence of F-L-M-I-D-Q-N-T-K. 54. The DNA sequence of claim 48 encoding a cancer recognition factor with an amino acid sequence of M-I-P-P-E-V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G- K. 55. The DNA sequence of claim 48 operably linked to control sequences effective in expresεing the DNA encoding the cancer recognition factor in compatible hoεt cellε. 56. A vector including the DNA of claim 51 capable of transfecting at least some of the host cells within which the DNA can be expressed. 57. Host cells transfected with the DNA vector of claim 52. 58. A procesε for producing a cancer recognition factor comprising the stepε of: (a) obtaining a body fluid from a donor afflicted with cancer; (b) εeparating a firεt fraction of the body fluid compriεing moleculeε having an apparent molecular weight, aε determined by ultrafiltration through an ultrafilter with a nominal molecular weight cutoff of greater than 1000 daltons, from a second fraction comprising molecules having an apparent molecular weight of leεs than 1000 daltons; and (c) purifying the second fractior. to obtain a substantially pure cancer recognition factor. 59. The procesε of claim 54 wherein the body fluid iε selected from the group conεiεting of peripheral blood, urine, plaεma, and cell aspirates. _ _ 60. The proceεs of claim 54 wherein the separation of the second fraction from the firεt fraction iε performed by ultrafiltration of the body fluid through an ultrafilter with a nominal 1000-dalton molecular weight cutoff. 61. The proceεε of claim 54 further compriεing the step of desalting the second fraction by loading the second fraction on a gel filtration column with a fractionation range of from 0 to about 700 daltons and capable of separating the salts therefrom, eluting the loaded material from the column with distilled water, and collecting that portion eluting at an elution volume between about 0.3 and about 0.5 times the total chromatographic bed volume, thereby increasing the specific activity of the cancer recognition factor in the collected desalted portion relative to the specific activity in the εecond fraction of claim 54. 62. The process of claim 57 further comprising the steps of: (a) loading the collected desalted portion on a gel filtration column having a fractionation range of from about 1500 daltons to about 30,000 daltons; (b) eluting the material loaded onto the column in step (a) from the column with a week aqueous solution of an ammonium salt; and (c) collecting that portion eluting at an elution volume between about 0.4 times and about 0.6 times the total chromatographic bed volume, thereby increasing the specific activity of the cancer recognition factor in the collected eluate relative to the specific activity in the collected desalted portion of claim 57. 63. The proceεs of claim 58 further compriεing the steps of: (a) loading the collected eluate on a diethylaminoethyl cellulose anion-exchange column; (b) eluting the material loaded onto the column in εtep (a) from the column with an increaεing concentration of an ammonium εalt; and (c) collecting that portion of the eluate eluting from the column at about 0.28 to about 0.31 M of the ammonium εalt, thereby increaεing the specific activity of the cancer recognition factor in the collected eluate relative to the specific activity in the collected eluate of claim 58. 64. The procesε of claim 59 further compriεing the εtepε of purifying the cancer recognition factor from the collected eluate of claim 59 to substantial homogeneity by reverse phase high preεsure chromatography. 65. A subεtantially purified cancer recognition factor produced by the proceεε of claim 54, 57, 58, 59, or 60. 66. A method of treating a cancer patient where at leaεt one of the body fluidε of the patient containε a cancer recognition factor, the factor being a peptide of at least 9 amino acid residueε including a core εequence of 9 amino acid reεidueε having an amphipathicity profile εubεtantially equivalent to that of the εequence F-L-M-I-D-Q-N-T-K, the method compriεing the steps of: (a) treating a body fluid containing the cancer recognition factor to reduce the in vivo effect of the factor by selectively inactivating it; and (b) returning the body fluid to the patient, thereby to enhance the resiεtance of the patient to the cancer. 67. The method of claim 62 wherein the body fluid iε peripheral blood and wherein the step of treating the body fluid compriseε dialyεis of the peripheral blood to remove peptides with an apparent molecular weight of leεε than 1000 daltons, whereby the cancer recognition factor is selectively inactivated by its removal from the blood. 68. The method of claim 62 wherein the εtep of treating the body fluid compriεeε neutralizing the cancer recognition factor in the body fluid with an antibody εpecific for the cancer recognition factor. 69. The method of claim 62 wherein the step of treating the body fluid compriseε neutralizing the cancer recognition factor in the body fluid with univalent antigen-binding fragmentε of an antibody specific for the cancer recognition factor, the univalent antigen-binding fragments being selected from Fab fragments and Fab' fragments. 70. The method of claim 62 wherein the step of treating the body fluid comprises inactivating the cancer recognition factor in the body fluid with an antisense peptide whose amino acid sequence is that encoded by the antisense strand of a DNA sequence whose sense strand encodes a cancer recognition factor of at leaεt 9 amino acid reεidues including a core sequence of 9 amino acid residueε having an amphipathicity profile εubεtantially equivalent to that of the sequence F-L-M-I-D-Q-N-T-K. 71. The method of claim 66 wherein the cancer recognition factor has the amino acid sequence F-L-M-I-D- Q-N-T-K. 72. The method of claim 66 wherein the cancer recognition factor has the amino acid εequence M-I-P-P-E- V-K-F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K-V-P-L-F-M-G-K. 73. The method of claim 62, 63, 64, 65, or 66 further comprising the step of treating the body fluid with a natural or synthetic protease inhibitor non- homologous with α-l-PI proteaεe inhibitor and non- homologous with any other protease inhibitor that is substantially inhibited by SCM factor, the protease inhibitor used for treatment being capable of inhibiting cancer-asεociated proteases protected against α-l-PI inhibition by SCM factor. 74. The method of claim 62, 63, 64, 65, or 66 further comprising the step of treating the patient with a clinically acceptable metabolic inhibitor that causes a decrease in production of the SCM factor by tumor cells. 75. The method of claim 70 wherein the metabolic inhibitor iε ascorbic acid. 76. A method of imaging cancer cells comprising the stepε of: (a) labeling the antibody of claim 38 with an imaging εubεtance; and (b) utilizing the labeled antibody to image cancer cellε by expoεing the cancer cellε to the labeled antibody. 77. A method of imaging cancer cellε compriεing the εtepε of: (a) labeling the monoclonal antibody of claim 41 with an imaging εubstance; and (b) utilizing the labeled monoclonal antibody to image cancer cells by exposing the cancer cells to the labeled antibody. 78. A method of directing an anti-cancer substance to cancer cells compriεing the εtepε of: (a) tagging the antibody of claim 38 with the anti-cancer substance; and (b) administering the tagged antibody to a cancer patient so that the tagged antibody can bind to cancer cells of the patient thereby directing the anti- cancer substance to the cancer cells. 79. A method of directing an anti-cancer substance to cancer cells comprising the stepε of: (a) tagging the monoclonal antibody of claim 41 with the anti-cancer εubεtance; and (b) administering the tagged monoclonal antibody to a cancer patient εo that the tagged antibody can bind to cancer cellε of the patient thereby directing the anti-cancer substance to the cancer cells. 80. A subεtantially purified peptide of at leaεt 22 amino acid residues including an natural killer- εuppreεεive (NK-εuppressive) εequence of F-X 9 -K-P-F-X 13 -F- X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K-X 23 -P-X 2S -F-M-G-K, wherein X 13 , X 15 , X 17 , X^, and X 25 are each independently selected from the group consisting of I, L, and V; X 18 is selected from the group consiεting of D and E; X 9 , X 19 and X 20 are each independently εelected from the group conεisting of Q and N; and X 21 is selected from the group consiεting of S and T, the peptide having NK-εuppreεsive activity. 81. The peptide of claim 76 wherein the NK- suppressive sequence is F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K. 82. The peptide of claim 77 wherein the peptide has the sequence F-N-K-P-F-V-F-L-M-I-D-Q-N-T-K. 83. A method for assesεing the effectiveness of an anti-cancer agent capable of inhibiting the growth of malignant cells in a cell culture, the cell culture including both lymphocytes exhibiting NK activity and malignant cells, the method comprising the steps of: (a) incubating the cell culture with the substantially purified NK-suppreεsive peptide of claim 76 in a quantity sufficient to substantially suppress the NK activity of the lymphocytes of the cell culture; (b) adding the anti-cancer agent to the cell culture in a quantity suf icient to inhibit the growth of the malignant cells; and (c) determining the effect of the anti- cancer agent on the malignant cellε by observing the inhibition of growth of the malignant cells caused by the anti-cancer agent in the essential absence of NK activity caused by the lymphocytes. 84. A method of suppreεsing the NK activity of lymphocytes comprising administering to the lymphocytes the subεtantially purified peptide of claim 76 in a quantity εufficient to εubstantially suppresε the NK activity of the lymphocytes as measured by the in vitro lysis of K562 cells. 85. A method of reversing the NK-suppresεive action of SCM factor in vivo compriεing adminiεtering to a patient at least one of whose body fluids contains SCM factor a SCM-factor-inhibiting subεtance εelected from the group conεiεting of antibodies to SCM factor, univalent antigen-binding fragments of antibodies to SCM factor, and antisense peptides whose amino acid εequences are those encoded by the antisense strand of DNA sequences whose sense strand encodes a NK-suppreεεive sequence of F-X 9 -K-P-F-X 13 -F-X 15 -M-X 17 -X 18 -X 19 -X 20 -X 21 -K-X 23 -P- X^-F-M-G-K, wherein X 13 , X 15 , X 17 , X s , and X 25 are each independently selected from the group consisting of I, L, and V; X 18 is selected from the group consiεting of D and E; X 9 , X 19 and X 20 are each independently selected from the group consisting of Q and N; and X 21 is selected from the group consisting of S and T, in a quantity sufficient to εubstantially reverεe the NK-suppressive action of the SCM factor and subεtantially reεtore normal NK activity of lymphocyteε of the patient aε measured by in vitro lysis of K562 cells by the lymphocytes. 86. A method for inducing immunosuppression in vivo, comprising the εtep of adminiεtering an immunosuppressive fraction selected from the group consisting of the subεtantially purified cancer recognition factor of claim l, 13, 14, or 31 and the εubstantially purified peptide of claim 76, alone or in combination with a pharmaceutically acceptable carrier in a quantity sufficient to create a degree of immunosuppreεεion capable of enhancing allograft survival. 87. A method for determining the εensitization of SCM-responding lymphocytes to SCM factor comprising the εteps of: (a) isolating SCM-responding lymphocytes; (b) washing the isolated SCM-responding lymphocytes; (c) incubating the isolated SCM- responding lymphocytes with a saturating quantity of the subεtantially purified cancer recognition factor of claim 1, 13, 14, or 31 labeled with a detectable label; and (d) determining the extent of the binding of the labeled cancer recognition factor to the SCM- reεponding lymphocyteε in order to determine the preεence of receptorε εpecific for SCM factor on the lymphocyteε and the εensitization of the lymphocytes to SCM factor.

Inventors: CERCEK BORIS, CERCEK LEA, CERCEK, BORIS, CERCEK, LEA
Applicants: CERCEK BORIS, CERCEK LEA, CERCEK, BORIS, CERCEK, LEA
Application year: 1991
Main classification: G01N33
IPC codes: A61K38, A61K39, A61K49, A61P35, C07K1, C07K7, C07K14, C07K16, C12N1, C12N15, C12P21, G01N33