Patent Publication Number: US-2022213163-A1

Title: Il-2 chimeric proteins for immunosuppression

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Bypass Continuation of PCT Patent Application No. PCT/IL2020/051029 having International filing date of Sep. 22, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/903,855 filed Sep. 22, 2019, the contents of which are all incorporated herein by reference in their entirety. 
    
    
     FIELD OF INVENTION 
     The present invention is in the field of immunosuppression. 
     BACKGROUND OF THE INVENTION 
     Low does IL-2 treatment has been shown to be effective in the treatment of inflammation and autoimmunity. This is due to low does IL-2 stimulating expansion of the regulatory T cell (Treg) population. However, IL-2 has an extremely short half-life in the blood. In order to keep a low dose of IL-2 present in the blood, recombinant wild-type IL-2 would need to be administered at a very high frequency, potentially daily. Further, IL-2 fusion proteins comprising an IgG fragment, though shown to increase half-life have also been shown to result in regulatory T-cell specific death. The literature regarding use of IgG fragments for IL-2 half-life extension is contradictory in this respect. 
     Chimeric IL-2 molecules that are effective in increasing serum half-life and inducing expansion of the Treg population are greatly needed. Further, IL-2 molecules that specifically enhance Treg proliferation, but do not impact cytotoxic CD8 +  cells would be extremely valuable in the treatment of inflammation and autoimmunity. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods of increasing regulatory T cell (Treg) proliferation and/or number in a subject as well as treating inflammatory and autoimmune diseases by administering an IL-2 chimeric molecule with increased serum half-life as compared to wild-type IL-2. 
     According to a first aspect, there is provided a method of increasing regulatory T cell (Treg) number in a subject in need thereof, the method comprising administering to the subject an interleukin-2 (IL-2) chimeric molecule characterized by increased serum half-life as compared to a wild-type IL-2 molecule and wherein the IL-2 chimeric molecule lacks an immunoglobulin moiety, thereby increasing Treg proliferation in a subject. 
     According to some embodiments, the administering comprises administering a low dose of the IL-2 chimeric molecule, wherein the low dose is a dose that does not activate CD8 +  cell proliferation, natural killer (NK) cell proliferation, or both. 
     According to some embodiments, the increasing Treg number comprises increasing Treg proliferation. 
     According to some embodiments, the method further comprises at least one of: increasing CD4+/CD25+ cell number in the subject, increasing CD8 + /CD25+ cell number in the subject, increasing CD8 + /CD25+/FoxP3+ cell number in the subject and not increasing CD69 positive immune cells in the subject. 
     According to some embodiments, the increasing Treg number comprises treating inflammation. 
     According to some embodiments, the inflammation is an inflammatory disease or an autoimmune disease. 
     v the autoimmune disease is selected from inflammatory bowel disease (IBD), and arthritis. 
     According to some embodiments, the increased serum half-life comprises at least a 10 times longer clearance half-life as compared to wild-type IL-2. 
     According to some embodiments, the chimeric molecule is further characterized by increased signaling through IL-2 receptor (IL-2R) upon binding as compared to wild-type IL-2, increased proliferation induction of CTLL-2 cells upon binding as compared to wild-type IL-2, or both. 
     According to some embodiments, the IL-2 is selected from wild-type IL-2, IL-2 mutated to increase binding to Tregs, IL-2 mutated to decrease binding to CD8 +  T-cells and natural killer cells, IL-2 mutated to increase binding to IL-2R gamma (IL-2Rγ) and IL-2 mutated to decrease binding to IL-2R beta (IL-2Rβ). 
     According to some embodiments, the wild-type IL-2 comprises SEQ ID NO: 13 and wherein the mutated IL-2 comprises SEQ ID NO: 8. 
     According to some embodiments, the chimeric molecule binds CD25 with higher affinity that wild-type IL-2. 
     According to some embodiments, the chimeric molecule comprises a NKp44 hinge region moiety. 
     According to some embodiments, the moiety is selected from SEQ ID NO: 2 and SEQ ID NO: 3. 
     According to some embodiments, the NKp44 moiety is attached to an N-terminus, C-terminus or both of the IL-2. 
     According to some embodiments, the chimeric molecule comprises a NKp44 moiety attached to an N-terminus and a C-terminus of the IL-2. 
     According to some embodiments, the NKp44 moiety is glycosylated. 
     According to some embodiments, the chimeric molecule comprises an amino acid sequence selected from SEQ ID NO: 4, 5, 6, 7, 14, 15, 16, and 17. 
     According to some embodiments, the chimeric molecule comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 6 and SEQ ID NO: 14. 
     According to some embodiments, the chimeric molecule comprises SEQ ID NO: 6. 
     According to some embodiments, the administering is administering a low dose of the IL-2 chimeric molecule, wherein the low dose is the equivalent number of international units (IU)/day of the IL-2 chimeric molecule as the IU/day for low dose wild-type IL-2 therapy. 
     According to some embodiments, the low dose is a dose below 5×10{circumflex over ( )}6 IU/day. 
     According to some embodiments, the administering is administering a reduced dosing regimen as compared to wild-type IL-2 therapy, and wherein the reduced dosing regimen comprises dosing less frequently that daily. 
     According to some embodiments, the reduced dosing regimen comprises dosing every 2-4 days. 
     According to another aspect, there is provided a chimeric molecule comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 14-18. 
     According to some embodiments, the chimeric molecule consists of the amino acid sequence of SEQ ID NO: 14. 
     According to another aspect, there is provided a pharmaceutical composition comprising a chimeric molecule of the invention and a pharmaceutically acceptable carrier, excipient or adjuvant. 
     According to another aspect, there is provided a IL-2 chimeric molecule characterized by increased serum half-life as compared to a wild-type IL-2 molecule and lacking an immunoglobulin domain for use in increasing regulatory T cell (T reg ) number in a subject in need thereof. 
     Further embodiments and the full scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
         FIGS. 1A-1E : Protein production and analysis. ( 1 A) A scheme describing the protein structure, including the highly glycosylated flanking sequences. ( 1 B) Post purification SDS-PAGE gel showing protein size is about 50 kDa, twice as much as calculated from AA sequence (26 kDa), due to glycosylation. ( 1 C) A representative ELISA binding curve (fitted to 4-parameter logistic), showing similar binding curves and EC 50  values for recombinant IL-2 and the S2A chimera. ( 1 D) A representative CTLL-2 proliferation test, done using MTT assay (fitted to 4-parameter logistic) showing a typical lower ED 50  for S2A (higher specific activity). ( 1 E) Summary of CTLL-2 MTT assays (n=5) showing a statistically significant (Mann-Whitney u-test) and relatively consistent difference between S2A and Proleukin in respect to ED 50 . * p-value &lt;0.05. 
         FIGS. 2A-2B : PKPD analysis. ( 2 A) Mice (n=5) were injected with Proleukin and S2A subcutaneously, levels of cytokines were measured over time, in blood retrieved from tail, using ELISA. Presented in tables are the calculated results for a one-compartment model. Showing a significantly shorter clearance time for Proleukin compare to S2A. As well as smaller AUC value, indicating lower bioavailability for Proleukin. ( 2 B) Line graph of cytokine levels measured over time for injected S2A, S2S and A2A at various concentrations. 
         FIGS. 3A-3C : Induction of T Reg  by S2A inoculation. Mice (n=5) were inoculated with 30,000 units of S2A, Vehicle and the same volume of vehicle twice. PBMCs were isolated 3 days after each inoculation, and stained for C45, CD4, CD8, CD25, FoxP3 and CD69. ( 3 A) A representative scheme of dot plots and histograms describing the gating strategy. FACS performed on Gallios Flow Cytometer—Beckman Coulter, and analysis was carried out on Kaluza. ( 3 B) A representative (1 experiment of 2) aggregation of FACS data from day 3 (3 days after 1 st  inoculation). Data is arranged according to lineage (CD4 +  and CD8 + ) and presented as a percentage of the indicated population on the y-axis. A very significant induction of the classic T Reg  phenotype (CD4 + CD25 + FoxP3 + ) was detected in S2A inoculated mice (4.8 folds compared to vehicle). ( 3 C) Aggregation of FACS data from day 7 (3 days after 2nd inoculation). Data is arranged in the same manner as  3 B. A significant induction of CD4 + CD25 +  was detected (4.4 folds) in the S2A inoculated mice, as well as induction of the classical T Reg  phenotype (6.1 folds). Error bars represent 95% CI. CD4 + CD25 + CD69 +  population was dismal. * p-value &lt;0.05, ** p-value &lt;0.005, *** p-value &lt;0.0005. 
         FIGS. 4A-4E : Enhancement of B16 growth and T Reg  frequency in Tumor micro-environment (TME). Mice (n=8) were injected with 100,000 B16BL8 cells i.v. and after 6 days a session of 3 inoculations, every 4 days was initiated. 30,000 units of S2A, Proleukin and the corresponding volume of vehicle were injected at each inoculation. At the 4 th  day after the last inoculation, mice were sacrificed, and lungs were removed. ( 4 A) A representative example of a lung covered with B16 metastasis nodules. All lungs across all treatments exhibited melanotic nodules. ( 4 B) To assess metastasis formation, lungs were weighed. A statistically significant difference of 1.3 folds (p-value &lt;0.005) and 1.5 folds (p-value &lt;0.0005) was measured between the mass of S2A treated lungs and Proleukin and vehicle respectively (continuous line—mean, dashed line—median). ( 4 C) Micrographs of lungs fixed, embedded, cut and stained for FoxP3 in addition to H&amp;E, in-order to examine the TME. ( 4 D) Box plot showing samples prepared from S2A treated mice showed higher frequency of FoxP3 positive cells (10 folds, p-value &lt;0.005), indicating higher infiltration of T Regs  into the TME. ( 4 E) FACS analysis of PBMCs isolated at the day of sacrifice, arranged according to lineage, and presented as percentage of the population noted on the y-axis. Error bars represent 95% CI. * p-value &lt;0.05, ** p-value &lt;0.005, *** p-value &lt;0.0005. 
         FIGS. 5A-5F : S2A generates a protective effect against DSS induced colitis. Mice (n=12) were given water supplemented with DSS for a week, which induces colitis, during which mice were inoculated twice (day 2 and 6) with 30,000 units of S2A, Proleukin and a corresponding volume of vehicle. After this period, half of the mice were sacrificed, and half were allowed to enter a recovery period of a week before sacrifice. ( 5 A) A representative photograph of colons removed from sacrificed mice, at the end of DSS period (day 8) and at the end of recovery period (day 16). ( 5 B) Colon length was measured, showing a significant statistical difference between S2A treated group and vehicle at day 8 (p-value &lt;0.05), as well as a statistically significant difference at day 16 between S2A treated group and both Proleukin treated group (p-value &lt;0.05) and vehicle (p-value &lt;0.005). Presented is a representative experiment of 2 (continuous line—mean, dashed line—median). ( 5 C) Mice were weighed throughout the experiment, and summary of weight loss as percentage of original weight was plotted against time (▾ indicates inoculations). Two-way ANOVA was calculated using SPSS, where the combined effect of treatment and time was found to be significant (p-value &lt;0.0005). Post-hoc test revealed S2A was significantly different from Proleukin (p-value &lt;0.05) and vehicle (p-value &lt;0.0005). ( 5 D) In addition to weight loss, clinical data (diarrhea and anal bleeding) was collected and factored with weight loss to compile the clinical score, summary of which is plotted against time (▾ indicates inoculations). Two-way ANOVA was carried in SPSS and the combined effect of treatments and time was found to be significant (p-value &lt;0.0005). Post-hoc test showed a significant difference between S2A and vehicle but not with Proleukin. However, when considering only the recovery period, statistical significance arises between S2A and proleukin (p-value &lt;0.005). ( 5 E- 5 F) PBMCs were isolated during sacrifice day: ( 5 E) day 8 and ( 5 F) day 16. Summary of FACS analysis is arranged according to lineage and presented as a percentage of the population noted on the y-axis. A significant change was found on the classical T Reg  phnotype population (CD4 + CD25 + FoxP3) on day 8. Error bars represent 95% CI. * p-value &lt;0.05, ** p-value &lt;0.005, *** p-value &lt;0.0005. 
         FIGS. 6A-6C : S2A attenuates the effects of rheumatoid arthritis in (RA) IL-1ra KO model. IL-1ra KO mice spontaneously develop RA at age of 3-6 weeks. Mice (n=5) were inoculated with 100,000 units every 3 days for a total of 7 inoculations. ( 6 A) Representative examples for the RA phenotype (inflamed and swollen hind-limb joints). ( 6 B) Joints width was measured, normalized to vehicle and plotted against time (▾ indicates inoculations). Two-way ANOVA was performed on data, and while combined effect was not statistically significant, the treatment component was significant (p-value &lt;0.0005). ( 6 C) At day 21 PBMCs were isolated. FACS analysis is arranged according to lineage and presented as a percentage of the population noted on the y-axis. A significant change in the induction of CD4+CD25+ subset of CD45+(6.4 folds) between the S2A treated group and the vehicle group. A smaller significant change was measured in the levels of the classical T Reg  population (2.1 folds) between the S2A treated group and the vehicle group. Error bars represent 95% CI. * p-value &lt;0.05, ** p-value &lt;0.005, *** p-value &lt;0.0005. 
         FIGS. 7A-7C : Mice (n=3) were inoculated with 25,000, 50,000 or 100,00 units of S2A, 25,000 or 50,000 units of N88D IL-2 and the same volume of vehicle. PBMCs were isolated 3 days after each inoculation, and stained for C45, CD4, CD8, CD25, and FoxP3. ( 7 A- 7 C) Bar graphs showing representative aggregation of FACS data from day 3 (left) and day 7 (right). Data is arranged according to lineage (CD4 +  and CD8 + ) and presented as a percentage of the indicated population on the y-axis. ( 7 A) Total CD4 and CD8 numbers were unchanged by N88D or S2A. ( 7 B) A very significant induction of CD25 positive cells is induced by S2A, while a smaller induction is produced by N88D. ( 7 C) The classic T Reg  phenotype (CD4 + CD25 + FoxP3 + ) was greatly enhanced in S2A inoculated mice and minorly enhanced in N88D inoculated mice. * p-value &lt;0.05, ** p-value &lt;0.005, *** p-value &lt;0.0005. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention, in some embodiments, provides methods of increasing regulatory T cell (Treg) number in a subject. The present invention further concerns a method of treating inflammatory and autoimmune disease. 
     The invention is based, at least in part, on the surprising finding that IL-2 chimeras comprising non-IgG half-life extending moieties, by keeping a constant low level of IL-2 in circulation, are ideal for increasing T reg  proliferation in a subject, while at the same time not activating or minimally activating CD8+ T cell or natural killer (NK) cell proliferation. It was further surprisingly found that these molecules unexpectedly induce a stronger signal through the IL-2 receptor (IL-2R), and are thus superior at inducing T reg  proliferation, reducing inflammation and treating autoimmune/inflammatory disorders. 
     By a first aspect, there is provided a method of increasing T regs  in a subject in need thereof, the method comprising administering to the subject an interleukin-2 (IL-2) chimeric molecule characterized by increased serum half-life, thereby increasing T regs  in a subject. 
     In some embodiments, a T cell is a CD3 positive cell. In some embodiments, a T cell is a CD45 positive cell. In some embodiments, a helper T cell is a CD4 positive (CD4+) cell. In some embodiments, a cytotoxic T cell is a CD8 positive (CD8+) cell. In some embodiments, a T reg  is CD4+. In some embodiments, a T reg  is CD25 positive (CD25+). In some embodiments, a T reg  is FOXP3 positive (FoxP3+). In some embodiments, a T reg  is CD69 negative (CD69-). In some embodiments, a T reg  is CD8 negative (CD8-). In some embodiments, a non-canonical T reg  is CD8+. In some embodiments, a Treg is CD127 positive. In some embodiments, a T reg  is CD152 positive. In some embodiments, a Treg is CD4+/CD25+/FoxP3+. Regulatory T cells are well known in the art and several markers, both surface and nuclear, are known for this cell type. Commercial kits for staining T reg s (such as from Abcam) and for isolation of T regs  (such as from Miltenyi Biiotec) are available. 
     In some embodiments, increasing T regs  comprises increasing T reg  number. In some embodiments, increasing T regs  comprises increasing T reg  proliferation. In some embodiments, increasing T regs  is increasing T reg  proliferation. In some embodiments, increasing T reg s comprises increasing T reg  localization to a site of inflammation or immune response. In some embodiments, increasing T regs  is increasing the percentage of CD4 positive T cells that are T reg s. In some embodiments, increasing T regs  is increasing the percentage of CD4/CD25 positive T cells that are FoxP3 positive. In some embodiments, increasing T regs  is increasing the production of T reg s. In some embodiments, increasing T regs  is increasing T helper cells adopting the Treg cell fate. In some embodiments, the increase is an in vivo increase. In some embodiments, the increase is an in vitro increase. 
     Increased proliferation can be measured by any assay known in the art, including assays described herein below. In some embodiments, increased proliferation is measured in blood. In some embodiments, increased proliferation is measured in serum. In some embodiments, increased proliferation is measured in a target organ. In some embodiments, the target organ is an organ comprising inflammation. In some embodiments, the organ is a diseased organ. In some embodiments, the organ is an organ undergoing autoimmune attack. In some embodiments, the organ is selected from the bowel, an intestine, a joint, blood, serum, the pancreas, muscle, skin, the thyroid, the nervous system, the brain, a lymph node, a kidney, a lung and the heart. 
     In some embodiments, the increase is a substantial increase. In some embodiments, the increase is a significant increase. In some embodiments, significant is statistically significant. In some embodiments, the increase is an increase of at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450 or 500% increase. Each possibility represents a separate embodiment of the invention. In some embodiments, the increase is a localized increase. In some embodiments, the increase is a systemic increase. In some embodiments, the increase is localized in a target organ. In some embodiments, the increase is as compared to the subject before the administration. In some embodiments, the increase is as compared to a healthy control. In some embodiments, the increase is as compared to a control with the same condition/disease as the subject. In some embodiments, the increase is as compared to a predetermined baseline or threshold. In some embodiments, the increase is as compared to a subject administered non-chimeric IL-2. In some embodiments, the increase is as compared to a subject administered chimeric IL-2 comprising an immunoglobulin moiety. In some embodiments, the increase is as compared to a subject administered IL-2 comprising a N88D mutation. In some embodiments, the administering the chimeric IL-2 of the invention and administering another IL-2 is at an equivalent dosage. In some embodiments, the equivalent dosage is the same units (U) per day. In some embodiments, the units are international units (IU). It will be understood that the same units per day need not be exactly the same amount per day but could average to the same units per day. For example, a dose of X unit per day is equivalent to a dose of 2× units every other day or 7× units weekly. 
     In some embodiments, the method further comprises confirming an increase in T reg  proliferation. In some embodiments, the method further comprises confirming an increase in T reg  number. In some embodiments, the method further comprises confirming an increase in T reg  percentage. In some embodiments, the method comprises confirming increased Tregs. In some embodiments, the method further comprises receiving a sample from the subject. In some embodiments, the confirming is in the sample. In some embodiments, measuring increased proliferation comprises measuring T reg  numbers and comparing it to T reg  numbers in a non-treated setting. In some embodiments, measuring proliferation comprises extracting a biological sample from the subject and measuring T reg  number. In some embodiments, the biological sample is selected from blood, plasma, lymph, urine, semen, stool, breast milk, cerebral-spinal fluid, lung aspirate and a biopsy. In some embodiments, the biopsy is from a target organ. Counting T regs  in a sample can be performed by any method known in the art, including but not limited to flow cytometric analysis of cells in the sample. T reg  markers can be measured on cells of the sample and the T reg  percentage/number calculated from the staining. 
     In some embodiments, the method does not comprise increasing proliferation of a cytotoxic cell type. In some embodiments, the method does not comprise substantial increasing of proliferation of a cytotoxic cell type. In some embodiments, a cytotoxic cell type is selected from a CD8+ T cell and an NK cell. In some embodiments a cytotoxic cell is an NK cell. In some embodiments, a cytotoxic cell is a CD8+ T cell. In some embodiments, a cytotoxic cell is a cytotoxic T cell. In some embodiments, a substantial increase is an increase of greater than 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100% in proliferation. Each possibility represents a separate embodiment of the invention. 
     In some embodiments, the method does not comprise increasing proliferation of CD4 positive T cells. In some embodiments, the method does not comprise increasing proliferation of the entire CD4 positive population. In some embodiments, the method comprises increasing the percentage of CD4 positive T cells that are T regs . In some embodiments, the method comprises decreasing the number of CD4 positive T cells that are not T reg s. 
     In some embodiments, the method does not activate an immune response. In some embodiments, the method does not increase an ongoing immune response. In some embodiments, the method decreases an immune response. In some embodiments, the method decreases inflammation. In some embodiments, the inflammation is systemic inflammation. In some embodiments, the inflammation is localized inflammation. In some embodiments, the method comprises administering a low dose of the IL-2 chimeric molecule. In some embodiments, the method comprises administering a dose that is below low dose IL-2 therapy. In some embodiments, the method comprises administering a dose below the low dose administered to treat inflammation and/or autoimmune disease. In some embodiments, low dose is a dose that does not activate CD8 cell proliferation, natural killer cell proliferation or both. 
     In some embodiments, administering is administering a low dose. In some embodiments, the dose is a therapeutically effective dose. In some embodiments, low dose administration is equivalent to low dose administration in low dose wild-type IL-2 therapy. In some embodiments, equivalent is equivalency in the units/day of the dose of IL-2. In some embodiments, the U/day of the IL-2 is equivalent to the U/day of the chimeric IL-2. In some embodiments, low dose is a dose at or below 10, 9, 8, 7, 6, 5, 4, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.75, 0.7, 0.6, 0.5, 0.4, 0.3, 0.25, 0.2, 0.1, 0.08, 0.05, 0.03, and 0.01×10{circumflex over ( )}6 U/day. Each possibility represents a separate embodiment of the invention. In some embodiments, low dose is a dose at or below 5×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 1×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 0.5×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 0.3×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 0.1×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 0.08×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 0.05×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 0.03×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose at or below 0.01×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 10, 9, 8, 7, 6, 5, 4, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.75, 0.7, 0.6, 0.5, 0.4, 0.3, 0.25, 0.2, 0.1, 0.08, 0.05, 0.03, and 0.01×10{circumflex over ( )}6 U/day. Each possibility represents a separate embodiment of the invention. In some embodiments, low dose is a dose of about 5×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 1×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 0.5×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 0.3×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 0.1×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose 0.08×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 0.05×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 0.03×10{circumflex over ( )}6 U/day. In some embodiments, low dose is a dose of about 0.01×10{circumflex over ( )}6 U/day. It will be understood that a low dose must be a therapeutically effective dose and thus a lower limit is provided due to the requirement that it is effective. In some embodiments, the dose is at or above 10, 9, 8, 7, 6, 5, 4, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.75, 0.7, 0.6, 0.5, 0.4, 0.3, 0.25, 0.2, 0.1, 0.08, 0.05, 0.03, 0.01, 0.005, 0.001, 0.0005, and 0.0001×10{circumflex over ( )}6 U/day. Each possibility represents a separate embodiment of the invention. In some embodiments, the dose is at or above 0.01×10{circumflex over ( )}6 U/day. In some embodiments, the dose is at or above 0.03×10{circumflex over ( )}6 U/day. In some embodiments, the dose is at or above 0.05×10{circumflex over ( )}6 U/day. In some embodiments, the dose is at or above 0.001×10{circumflex over ( )}6 U/day. In some embodiments, the dose is at or above 0.005×10{circumflex over ( )}6 U/day. In some embodiments, the dose is at or above 0.0001×10{circumflex over ( )}6 U/day. In some embodiments, the dose is at or above 0.0005×10{circumflex over ( )}6 U/day. 
     In some embodiments, increasing T regs  comprises decreasing inflammation. In some embodiments, increasing T regs  comprises treating inflammation. In some embodiments, increasing T regs  comprises decreasing an immune response. In some embodiments, increasing T regs  comprises treating an autoimmune condition and/or disease. In some embodiments, the inflammation is an inflammatory disease. In some embodiments, the inflammation is an autoimmune disease. In some embodiments, the immune response is an autoimmune condition and/or disease. 
     In some embodiments, an autoimmune disease is selected from inflammatory bowel disease (IBD), colitis, Crohn&#39;s disease, rheumatoid arthritis (RA), multiple sclerosis (MS), diabetes, lupus, psoriasis, Grave&#39;s disease, celiac disease, Hashimoto&#39;s disease, myasthenia gravis, Guillain-Barré syndrome, scleroderma, asthma, alopecia, arthritis, neuromyelitis optica, demyelinating polyneuropathy and Behcet&#39;s syndrome. In some embodiments, IBD comprises colitis and Crohn&#39;s disease. In some embodiments, IBD comprises colitis. In some embodiments, the autoimmune disease is selected from IBD and RA. In some embodiments, the autoimmune disease is IBD. In some embodiments, the autoimmune disease is colitis. In some embodiments, the autoimmune disease is arthritis. In some embodiments, the autoimmune disease is RA. 
     In some embodiments, the administering comprises administering a low dose of the IL-2 chimeric molecule. In some embodiments, a low dose is a dose that does not activate an immune response. In some embodiments, a low dose is a dose that does not increase proliferation of a cytotoxic cell. In some embodiments, a low dose is a dose that does not activate proliferation of a cytotoxic cell. In some embodiments, a low dose is a dose at or below 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5.5, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.5. 0.4, 0.3, 0.2, 0.1, 0.05, 0.01, 0.005 or 0.001 million international units (MIU)/day. Each possibility represents a separate embodiment of the invention. In some embodiments, a low dose is a dose at or below 3.5 MIU/day. In some embodiments, a low dose is a dose at or below 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5.5, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.5. 0.4, 0.3, 0.2, 0.1, 0.05, 0.01, 0.005 or 0.001 MIU/meter{circumflex over ( )}2 (m 2 )/day. Each possibility represents a separate embodiment of the invention. In some embodiments, a low dose is a dose at or below 3.5 MIU/m 2 /day. In some embodiments, a low dose is less than 50,000 units per day. In some embodiments, a low dose is less than 100,000 units per day. In some embodiments, a low dose is at least 10,000 Units per day. In some embodiments, low dose is between 10,000 and 50,000 units per day. In some embodiments, low dose is between 10,000 and 100,000 units per day. In some embodiments low dose is about 10,000 units per day. In some embodiments low dose is about 30,000 units per day. In some embodiments low dose is about 50,000 units per day. In some embodiments low dose is about 100,000 units per day. 
     In some embodiments, the dose is below the standard therapeutic dose for treating an autoimmune disease. In some embodiments, the dose is below the standard therapeutic dose for treating cancer. In some embodiments, a dose is reduced due to the extended half-life of the chimeric molecule. In some embodiments, the dose is reduced due to the increased efficacy of the chimeric molecule. In some embodiments, a low dose is a dose that does not activate CD8 positive T cell proliferation. In some embodiments, a low dose is a dose that does not activate natural killer (NK) cell proliferation. 
     In some embodiments, a low dose comprises a less frequent dose as compared to standard therapy. In some embodiments, standard therapy is anti-cancer therapy. In some embodiments, standard therapy is autoimmune therapy. In some embodiments, standard therapy is low dose therapy. In some embodiments, a low does comprises a dose at most once a day, once every other day, once every third day, once every fourth day, twice a week, once every fifth day, once every sixth day, once a week, once every ten days, once every other week, once every three weeks, once every four weeks or once a month. Each possibility represents a separate embodiment of the invention. In some embodiment, low dose therapy is daily therapy. In some embodiments, the method comprises administering the therapy every other day. In some embodiments, the method comprises administering low dose therapy every other day. It will be understood by a skilled artisan that due to the short half life of IL-2 standard low dose therapy requires daily administration. Surprisingly, the half-life extended molecule could be administered every other day and still produce a superior result to recombinant 11-2 administered daily. In some embodiments, less frequent dosing is less frequently than daily. In some embodiments, less frequently than daily is every other day. In some embodiments, less frequently than daily is every 2 days. In some embodiments, less frequently than daily is every 3 days. In some embodiments, less frequently than daily is every 4 days. In some embodiments, less frequently than daily is every 5 days. In some embodiments, less frequently than daily is every 2-4 days. In some embodiments, less frequently than daily is every 2-5 days. In some embodiments, less frequently than daily is every 2 to 6 days. In some embodiments, less frequently than daily is every 2 to 7 days. In some embodiments, administering is a administering a reduced dosing regimen. In some embodiments, reduced is as compared to IL-2 therapy. In some embodiments, IL-2 therapy is low dose IL-2 therapy. In some embodiments, IL-2 is wild-type IL-2. In some embodiments, IL-2 is IL-2 comprising a N88D mutation. In some embodiments, IL-2 is a chimeric IL-2 linked to an immunoglobulin. In some embodiments, a reduced dosing regimen comprises dosing less frequently than daily. 
     In some embodiments, the frequency of dose is decreased due to the extended half-life of the chimeric molecule. In some embodiments, the frequency of dose is decreased due to the increased efficacy of the chimeric molecule. In some embodiments, the decrease in frequency is during a first course of the administering. In some embodiments, the first course is for 1, 2, 3, 4 or 5 weeks. Each possibility represents a separate embodiment of the invention. In some embodiments, the first course is for a week. In some embodiments, the decrease in dose is during a second course, or a maintenance period. In some embodiments, the second course is for 1 week, 2 weeks, 3, weeks, 4 weeks, 1 month, 2 months, 3 months, 4 months, 5 months, 6 months, 1 year, 2 years, 3 years, 4 years 5 years or indefinitely. Each possibility represents a separate embodiment of the invention. In some embodiments, the first period and second period use different doses. In some embodiments, the first and second period use the same dose. 
     As used herein, the terms “administering,” “administration,” and like terms refer to any method which, in sound medical practice, delivers a composition containing an active agent to a subject in such a manner as to provide a therapeutic effect. In some embodiments, administering is selected from oral, parenteral, subcutaneous, intravenous, anal, intramuscular, and intraperitoneal administration. In some embodiments, the administering comprises administering a therapeutically effective dose of the chimeric molecule. In some embodiments, the administering comprises administering a therapeutic composition comprising the chimeric molecule. In some embodiments, the therapeutic composition comprises a pharmaceutically acceptable carrier, excipient or adjuvant. In some embodiment, the therapeutic composition is formulated for systemic administration. 
     The dosage administered will be dependent upon the age, health, and weight of the recipient, kind of concurrent treatment, if any, frequency of treatment, and the nature of the effect desired. 
     As used herein, the term “carrier,” “excipient,” or “adjuvant” refers to any component of a pharmaceutical composition that is not the active agent. As used herein, the term “pharmaceutically acceptable carrier” refers to non-toxic, inert solid, semi-solid liquid filler, diluent, encapsulating material, formulation auxiliary of any type, or simply a sterile aqueous medium, such as saline. Some examples of the materials that can serve as pharmaceutically acceptable carriers are sugars, such as lactose, glucose and sucrose, starches such as corn starch and potato starch, cellulose and its derivatives such as sodium carboxymethyl cellulose, ethyl cellulose and cellulose acetate; powdered tragacanth; malt, gelatin, talc; excipients such as cocoa butter and suppository waxes; oils such as peanut oil, cottonseed oil, safflower oil, sesame oil, olive oil, corn oil and soybean oil; glycols, such as propylene glycol, polyols such as glycerin, sorbitol, mannitol and polyethylene glycol; esters such as ethyl oleate and ethyl laurate, agar; buffering agents such as magnesium hydroxide and aluminum hydroxide; alginic acid; pyrogen-free water; isotonic saline, Ringer&#39;s solution; ethyl alcohol and phosphate buffer solutions, as well as other non-toxic compatible substances used in pharmaceutical formulations. Some non-limiting examples of substances which can serve as a carrier herein include sugar, starch, cellulose and its derivatives, powered tragacanth, malt, gelatin, talc, stearic acid, magnesium stearate, calcium sulfate, vegetable oils, polyols, alginic acid, pyrogen-free water, isotonic saline, phosphate buffer solutions, cocoa butter (suppository base), emulsifier as well as other non-toxic pharmaceutically compatible substances used in other pharmaceutical formulations. Wetting agents and lubricants such as sodium lauryl sulfate, as well as coloring agents, flavoring agents, excipients, stabilizers, antioxidants, and preservatives may also be present. Any non-toxic, inert, and effective carrier may be used to formulate the compositions contemplated herein. Suitable pharmaceutically acceptable carriers, excipients, and diluents in this regard are well known to those of skill in the art, such as those described in The Merck Index, Thirteenth Edition, Budavari et al., Eds., Merck &amp; Co., Inc., Rahway, N.J. (2001); the CTFA (Cosmetic, Toiletry, and Fragrance Association) International Cosmetic Ingredient Dictionary and Handbook, Tenth Edition (2004); and the “Inactive Ingredient Guide,” U.S. Food and Drug Administration (FDA) Center for Drug Evaluation and Research (CDER) Office of Management, the contents of all of which are hereby incorporated by reference in their entirety. Examples of pharmaceutically acceptable excipients, carriers and diluents useful in the present compositions include distilled water, physiological saline, Ringer&#39;s solution, dextrose solution, Hank&#39;s solution, and DMSO. These additional inactive components, as well as effective formulations and administration procedures, are well known in the art and are described in standard textbooks, such as Goodman and Gillman&#39;s: The Pharmacological Bases of Therapeutics, 8th Ed., Gilman et al. Eds. Pergamon Press (1990); Remington&#39;s Pharmaceutical Sciences, 18th Ed., Mack Publishing Co., Easton, Pa. (1990); and Remington: The Science and Practice of Pharmacy, 21st Ed., Lippincott Williams &amp; Wilkins, Philadelphia, Pa., (2005), each of which is incorporated by reference herein in its entirety. The presently described composition may also be contained in artificially created structures such as liposomes, ISCOMS, slow-releasing particles, and other vehicles which increase the half-life of the peptides or polypeptides in serum. Liposomes include emulsions, foams, micelies, insoluble monolayers, liquid crystals, phospholipid dispersions, lamellar layers and the like. Liposomes for use with the presently described peptides are formed from standard vesicle-forming lipids which generally include neutral and negatively charged phospholipids and a sterol, such as cholesterol. The selection of lipids is generally determined by considerations such as liposome size and stability in the blood. A variety of methods are available for preparing liposomes as reviewed, for example, by Coligan, J. E. et al, Current Protocols in Protein Science, 1999, John Wiley &amp; Sons, Inc., New York, and see also U.S. Pat. Nos. 4,235,871, 4,501,728, 4,837,028, and 5,019,369. 
     The carrier may comprise, in total, from about 0.1% to about 99.99999% by weight of the pharmaceutical compositions presented herein. 
     The term “chimera” refers to a polypeptide formed by the joining of two or more peptides through a peptide bond formed between the amino terminus of one peptide and the carboxyl terminus of another peptide. The chimera may be formed by a chemical coupling of the constituent peptides or it may be expressed as a single polypeptide fusion protein from a nucleic acid sequence encoding the single contiguous conjugate. 
     As used herein, the terms “peptide”, “polypeptide” and “protein” are used interchangeably to refer to a polymer of amino acid residues. The terms “peptide”, “polypeptide” and “protein” as used herein encompass native peptides, peptidomimetics (typically including non-peptide bonds or other synthetic modifications) and the peptide analogs peptoids and semi-peptoids or any combination thereof. In another embodiment, the terms “peptide”, “polypeptide” and “protein” apply to amino acid polymers in which one or more amino acid residue is an artificial chemical analog of a corresponding naturally occurring amino acid. 
     In some embodiments, the chimeric molecule is characterized by an increased half-life. In some embodiments, the chimeric molecule is characterized by decreased decay. In some embodiments, the increased half-life is not mediated by Fc receptors. In some embodiments, the increased half-life is not mediated by Fc receptor, neonatal (FcRn). In some embodiments, the increased half-life is not mediated by recycling. In some embodiments, the chimeric molecule comprises an increased half-life. In some embodiments, the increased half-life is increased serum half-life. In some embodiments, the half-life is clearance half-life. In some embodiments, the half-life is blood clearance half-life. In some embodiments, the increase is as compared to IL-2. In some embodiments, the increase is as compared to a wild-type IL-2. In some embodiments, the increase is as compared to an IL-2 non-chimeric molecule. In some embodiments, the increase is as compared to an IL-2 molecule devoid of a non-IL-2 moiety. In some embodiments, the increase is as compared to a chimeric IL-2 molecule comprising an immunoglobulin. 
     In some embodiments, the increase comprises at least a 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, or 25 times longer half-life. Each possibility comprises a separate embodiment of the invention. In some embodiments, the increase comprises at least a 10 times longer half-life. Measuring half-life of a protein in a subject is well characterized in the art, and any method may be performed including those described hereinbelow. In some embodiments, measurements of molecule concentration are made a various time points in order to calculate half-life. 
     In some embodiments, the IL-2 is mammalian IL-2. In some embodiments, the IL-2 is human IL-2. In some embodiments, IL-2 comprises or consists of the amino acid sequence provided in accession number NP_000577.2 or XP_016863666.1 In some embodiments, IL-2 comprises or consists of the amino acid sequence provided in accession number NP_000577.2 In some embodiments, IL-2 is wild-type IL-2. In some embodiments, IL-2 comprises a signal peptide. In some embodiments, IL-2 does not comprise a signal peptide. In some embodiments, IL-2 is secreted IL-2. In some embodiments, IL-2 comprises or consists of the amino acid sequence MYRMQLLSCIALSLALVTNSAPTSSSTKKTQLQLEHLLLDLQMILNGINNYKNPKL TRMLTFKFYMPKKATELKHLQCLEEELKPLEEVLNLAQSKNFHLRPRDLISNINVI VLELKGSETTFMCEYADETATIVEFLNRWITFCQSIISTLT (SEQ ID NO: 12). In some embodiments, IL-2 lacks a signal peptide and comprises or consists of the amino acid sequence APTSSSTKKTQLQLEHLLLDLQMILNGINNYKNPKLTRMLTFKFYMPKKATELKH LQCLEEELKPLEEVLNLAQSKNFHLRPRDLISNINVIVLELKGSETTFMCEYADETA TIVEFLNRWITFCQSIISTLT (SEQ ID NO: 13). In some embodiments, IL-2 consists of SEQ ID NO: 12. In some embodiments, IL-2 consists of SEQ ID NO: 13. In some embodiments, secreted IL-2 consists of SEQ ID NO: 13. In some embodiments, the IL-2 signal peptide consists of the amino acid sequence MYRMQLLSCIALSLALVTNS (SEQ ID NO: 9). In some embodiments, the chimeric molecule further comprises a signal peptide at its N-terminus. In some embodiments, the signal peptide is the IL-2 signal peptide. 
     In some embodiments, the IL-2 is wild-type IL-2. In some embodiments, the IL-2 is not mutated. In some embodiments, the IL-2 is mutated IL-2. In some embodiments, the mutation is to increase binding to T reg s. In some embodiments, the mutation is to decrease binding to IL-2R beta (IL-2Rβ) chain. In some embodiments, the mutation is to decrease binding to IL-2R gamma (IL-2Rγ) chain. In some embodiments, the mutation is to decrease binding to IL-2R beta/gamma (IL-21βγ) receptor. In some embodiments, the mutation is to decrease binding to cytotoxic cells. In some embodiments, the mutation is to decrease binding to CD8+ T cells. In some embodiments, the mutation is to decrease binding to IL-2R alpha/beta (IL-2Rαβ) receptor. In some embodiments, the mutation is to increase binding to IL-2R alpha/beta (IL-2Rαβ) receptor. In some embodiments, the mutation is to increase binding to intermediate affinity IL-2R. In some embodiments, the mutation is to decrease binding to intermediate affinity IL-2R. In some embodiments, the mutation is to decrease binding to high affinity IL-2R. In some embodiments, the mutation is to increase binding to high affinity IL-2R. In some embodiments, the mutation is mutation of the asparagine (N) at position 88 of SEQ ID NO: 13. In some embodiments, the mutation is conversion of N88 to an aspartic acid (D). In some embodiments, the mutation is conversion of N88 to a lysine (K). 
     In some embodiments, the molecule is characterized by higher affinity binding to CD25. In some embodiments, the molecule is characterized by higher affinity binding to CD25. In some embodiments, the chimeric molecule binding CD25 with higher affinity. In some embodiments, the higher affinity is as compared to IL-2. In some embodiments, the higher affinity is as compared to wild-type IL-2. In some embodiments, the molecule is characterized by increased effect through IL-2R. In some embodiments, the molecule is characterized by increased signaling through IL-2R. In some embodiments, the increase is upon binding to IL-2R. In some embodiments, the increase is as compared to IL-2. In some embodiments, the increase is as compared to wild-type IL-2. In some embodiments, increased signaling comprises increased proliferation of a cell expressing IL-2R. In some embodiments, increased signaling comprises increased proliferation of CTLL-2 cells. In some embodiments, the molecule is characterized by increased proliferation of CTLL-2 cells. In some embodiments, increased signaling comprises increased proliferation of T reg s. Any method of measuring signaling through IL-2R may be used to characterize the molecule. Any method of measuring IL-2 dose may also be used. 
     In some embodiments, the method further comprises at least one of increasing CD4+/CD25+ cell number in said subject, increasing CD8+/CD25+ cell number in said subject, increasing CD45+/CD44+ cell number in said subject, increasing CD4+/CD25+/CD44+ cell number in said subject, increasing CD8+/CD25+/CD44+ cell number in said subject, not increasing CD8+/CD25+/FoxP3+ cell number in said subject, increasing CD8+/CD25+/FoxP3+ cell number in said subject and not increasing CD69 positive immune cells in said subject. In some embodiments, the method further comprises increasing CD4+/CD25+ cell number in said subject. In some embodiments, the method further comprises increasing CD8+/CD25+ cell number in said subject. In some embodiments, the method further comprises increasing CD45+/CD44+ cell number in said subject. In some embodiments, the method further comprises increasing CD4+/CD25+/CD44+ cell number in said subject. In some embodiments, the method further comprises increasing CD8+/CD25+/CD44+ cell number in said subject. In some embodiments, the method further comprises increasing CD8+/CD25+/FoxP3+ cell number in said subject. In some embodiments, the method further comprises not increasing CD8+/CD25+/FoxP3+ cell number in said subject. In some embodiments, the method further comprises not increasing CD69 positive immune cell number in said subject. In some embodiments, CD69 positive immune cells is CD8+/CD69+ cells. In some embodiments, CD69 positive immune cells is CD4+/CD69+ cells. In some embodiments, CD69 positive cells is CD69 positive Tregs. 
     In some embodiments, the chimeric molecule comprises a non-IL-2 moiety. In some embodiments, the moiety increases the half-life of the chimeric molecule. In some embodiments, the increase is as compared to wild-type IL-2. In some embodiments, the increase is as compared to IL-2 without the moiety. In some embodiments, the increase is as compared to IL-2 without a non-IL-2 moiety. In some embodiments, the non-IL-2 moiety is not an immunoglobulin moiety. In some embodiments, the chimeric molecule lacks, or is devoid of an immunoglobulin moiety. 
     The term “moiety”, as used herein, relates to a part of a molecule that may include either whole functional groups or parts of functional groups as substructures. The term “moiety” further means part of a molecule that exhibits a particular set of chemical and/or pharmacologic characteristics which are similar to the corresponding molecule. 
     Examples of moieties that extend half-life of proteins in vivo include, but are not limited to, IgG, human serum albumen (HSA), transferrin, CTP peptide, GLK, HAP, ELP repeat, PAS and XTEN. In some embodiments, the moiety extends half-life by a mechanism selected from increasing size, increasing hydrodynamic radius, increasing recycling, increasing negative charge and increasing glycosylation. In some embodiments, the moiety extends half-life by a mechanism selected from increasing size, increasing hydrodynamic radius, increasing negative charge and increasing glycosylation. In some embodiments, the moiety extends half-life by a mechanism selected from increasing negative charge and increasing glycosylation. In some embodiments, the moiety extends half-life by a mechanism selected from increasing negative charge and increasing glycosylation. In some embodiments, the glycosylation is O-linked glycosylation. In some embodiments, the glycosylation is predominantly O-linked glycosylation. 
     In some embodiments, an immunoglobulin moiety is an IgG. In some embodiments, the IgG is IgG1. In some embodiments, the IgG is IgG2. In some embodiments, the IgG is IgG3. In some embodiments, the IgG is IgG4. In some embodiments, the IgG is an IgG that binds FcRn. In some embodiments, the IgG is an IgG that does not bind FcRγ. In some embodiments, the immunoglobulin moiety is an antibody moiety. In some embodiments, the antibody moiety is an antigen binding domain. In some embodiments, the immunoglobulin moiety is an immunoglobulin domain. In some embodiments, the IgG is an IgG mutated to reduce antibody dependent cell cytotoxicity (ADCC). In some embodiments, the IgG is an IgG mutated to reduce complement dependent cytotoxicity (CDC). In some embodiments, the mutated IgG is a mutated IgG1. 
     In some embodiments, the moiety is attached to the N-terminus of IL-2. In some embodiments, the moiety is attached to the C-terminus of IL-2. In some embodiments, the moiety is attached to the N- or C-terminus of IL-2. In some embodiments, the moiety is attached to the N-terminus of IL-2, the C-terminus of IL-2 or both. In some embodiments, the moiety is attached to both the N-terminus and the C-terminus of IL-2. 
     In some embodiments, attached is linked. In some embodiments, linked is directly linked. In some embodiments, linked is linked by a linker. In some embodiments, the linker is a peptide linker. In some embodiments, the linker is a chemical linker. In some embodiments, the moiety and IL-2 are linked by an amino bond. In some embodiments, the moiety and IL-2 and part of a single amino acid chain. 
     In some embodiments, the moiety is an NKp44 moiety. In some embodiments, the NKp44 moiety is a NKp44 hinge region moiety. In some embodiments, the hinge region comprises amino acids 130 to 199 of NKp44. In some embodiments, the hinge region comprises amino acids 130 to 199 of SEQ ID NO: 1. In some embodiments, the moiety comprises at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 or 65 amino acids. Each possibility represents a separate embodiment of the invention. In some embodiments, the moiety comprises at most 20, 25, 30, 35, 40, 45, 50, 55, 60 or 65 amino acids. Each possibility represents a separate embodiment of the invention. In some embodiments, the moiety comprises at least 25 amino acids. In some embodiments, the moiety comprises at least 30 amino acids. In some embodiments, the moiety comprises at least 35 amino acids. In some embodiments, the moiety comprises at most 35 amino acids. In some embodiments, the moiety comprises at most 40 amino acids. In some embodiments, the moiety comprises at most 45 amino acids. 
     In some embodiments, the moiety is glycosylated. In some embodiments, the glycosylation is selected from N-linked and O-linked glycosylation. In some embodiments, the glycosylation is O-linked glycosylation. In some embodiments, the glycosylation is predominantly O-linked glycosylation. In some embodiments, the predominantly is at least 50, 55, 60, 65, 70, 75, 80, 85, 90, 93, 95, 97, 99 or 100% O-linked glycosylation. Each possibility represents a separate embodiment of the invention. 
     NKp44 is also known as natural cytotoxicity triggering receptor 2 (NCR2), as well as CD336, NK-p44, LY95 and dJ149M18.1. In some embodiments, the NKp44 is a human NKp44. In some embodiments, NkP44 comprises the amino acid sequence provided in GenBank accession No: NP001186438.1. In some embodiments, NKp44 comprises the amino acid sequence MAWRALHPLLLLLLLFPGSQAQSKAQVLQSVAGQTLTVRCQYPPTGSLYEKKGWC KEASALVCIRLVTSSKPRTMAWTSRFTIWDDPDAGFFTVTMTDLREEDSGHYWCRI YRPSDNSVSKSVRFYLVVSPASASTQTSWTPRDLVSSQTQTQSCVPPTAGARQAPES PSTIPVPSHPSSPLPVPLPSRPQNSTLRPGPAAPIALVPVFCGLLVAKSLVLSALLVWW VLRNRHMQHQGRSLLHPAQPRPQAHRHFPLSHRAPGGTYGGKP (SEQ ID NO: 1). In some embodiments, NKp44 consists of the amino acid sequence of SEQ ID NO: 1. 
     According to some embodiments, the moiety is a peptide of 20 to 50 amino acid residues, said peptide comprising a sequence derived from amino acids 130 to 199 of NKp44 (SEQ ID NO: 1). According to some embodiments, the invention provides a peptide of 20 to 50 amino acid residues derived from SEQ ID NO: 10. SEQ ID NO: 10 consists of the amino acid sequence SPASASTQTSWTPRDLVSSQTQTQSCVPPTAGARQAPESPSTIPVPSHPSSPLPVPLPS R PQNSTLRPGP. 
     In another embodiment, the moiety is a peptide, derived from amino acids 130 to 199 of SEQ ID NO: 1, wherein said peptide is devoid of: (a) a fragment consisting of amino acids 1 to 129, and (b) a fragment consisting of amino acids 200 to 270. 
     In another embodiment, the peptide comprises at least 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 contiguous amino acids derived from amino acids 130 to 199 of SEQ ID NO: 1. Each possibility represents a separate embodiment of the present invention. 
     In one embodiment, there is provided a peptide comprising at least 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 contiguous amino acids derived from amino acids 130 to 199 of SEQ ID NO: 1, wherein the peptide is devoid of: (a) a fragment consisting of amino acids 1 to 129, and (b) a fragment consisting of amino acids 200 to 270. Each possibility represents a separate embodiment of the present invention. 
     As used herein, the term “derived from” or “corresponding to” refers to construction of an amino acid sequence based on the knowledge of a sequence using any one of the suitable means known to one skilled in the art, e.g. chemical synthesis in accordance with standard protocols in the art. In one embodiment, a peptide derived from or corresponding to amino acids 130 to 199 of the sequence of NKp44 is a peptide based on residues 130 to 199 of SEQ ID NO: 1, or an analog, a variant, a derivative or a fragment thereof. In one embodiment, the peptide derived from or corresponding to amino acids 130 to 199 of SEQ ID NO: 1, has the amino acid sequence as set forth in SEQ ID NO: 10, or an analog, a variant, a derivative or a fragment thereof. 
     In another embodiment, the peptides comprising the amino acid sequence as set forth in SEQ ID NO: 10 have a length of less than 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, or 70 amino acids. Each possibility represents a separate embodiment of the present invention. In another embodiment, the peptide derived from NKp44 has a truncated form and/or is a fragment of SEQ ID NO: 10. In another embodiment, the peptide derived from NKp44 comprises at least 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 65, 66, 67, 68, 69 or 70 amino acids derived from SEQ ID NO: 10. Each possibility represents a separate embodiment of the invention. In another embodiment, the peptide derived from NKp44 comprises 20 to 70, 20 to 60, 20 to 55, 20 to 50, 20 to 40, 25 to 70, 25 to 60, 25 to 55, 25 to 50, 25 to 40, 30 to 70, 30 to 60, 30 to 50, or 30 to 40 amino acids derived from SEQ ID NO: 10. Each possibility represents a separate embodiment of the present invention. In another embodiment, the peptide derived from NKp44 is 20 to 70, 20 to 60, 20 to 55, 20 to 50, 20 to 40, 25 to 70, 25 to 60, 25 to 55, 25 to 50, 25 to 40, 30 to 70, 30 to 60, 30 to 50, or 30 to 40 amino acids long. Each possibility represents a separate embodiment of the present invention. 
     In one embodiment, the peptide derived from NKp44 comprises or consists of the amino acid sequence SPASASTQTSWTPRDLVSSQTQTQSCVPPTAGAR (SEQ ID NO: 2). SEQ ID NO: 2 is also known as the SPA moiety. In one embodiment, the peptide derived from NKp44 comprises or consists of the amino acid sequence QAPESPSTIPVPSHPSSPLPVPLPSRPQNSTLRPGP (SEQ ID NO: 3). SEQ ID NO: 3 is also known as the APE moiety. In one embodiment, the peptide derived from NKp4 comprises or consists of the amino acid sequence as set forth in SEQ ID NO: 2. In one embodiment, the truncated peptide derived from NKp44 comprises or consists of the amino acid sequence as set forth in SEQ ID NO: 3. 
     In some embodiments, the moiety is selected from SEQ ID NO: 2 and SEQ ID NO: 3. In some embodiments, the moiety is SEQ ID NO: 2. In some embodiments, the moiety is SEQ ID NO: 3. In some embodiments, SEQ ID NO:2 is attached to the N-terminus of IL-2. In some embodiments, SEQ ID NO: 2 is attached to the C-terminus of IL-2. In some embodiments, SEQ ID NO:3 is attached to the N-terminus of IL-2. In some embodiments, SEQ ID NO: 3 is attached to the C-terminus of IL-2. In some embodiments, SEQ ID NO: 2 is attached to both the N- and C-termini of IL-2 (the S2S molecule). In some embodiments, the chimeric molecule comprises the amino acid sequence of SEQ ID NO: 4 (the S2S molecule without a signal peptide). In some embodiments, the chimeric molecule consists of the amino acid sequence of SEQ ID NO: 4. In some embodiments, SEQ ID NO: 3 is attached to both the N- and C-termini of IL-2 (the A2A molecule). In some embodiments, the chimeric molecule comprises the amino acid sequence of SEQ ID NO: 5 (the A2A molecule without a signal peptide). In some embodiments, the chimeric molecule consists of the amino acid sequence of SEQ ID NO: 5. In some embodiments, SEQ ID NO: 2 is attached to the N- or C-terminus and SEQ ID NO: 3 is attached to the other terminus. In some embodiments, the chimeric molecule comprises an amino acid sequence selected from SEQ ID NO: 6 (the S2A molecule without a signal peptide) and SEQ ID NO: 7 (the A2S molecule without a signal peptide). In some embodiments, the chimeric molecule consists of an amino acid sequence selected from SEQ ID NO: 6 and SEQ ID NO: 7. In some embodiments, the chimeric molecule comprises the amino acid sequence of SEQ ID NO: 6. In some embodiments, the chimeric molecule consists of the amino acid sequence of SEQ ID NO: 6. In some embodiments, the chimeric molecule comprises the amino acid sequence of SEQ ID NO: 7. In some embodiments, the chimeric molecule consists of the amino acid sequence of SEQ ID NO: 7. In some embodiments, the chimeric molecule is S2A. In some embodiments, S2A comprises a signal peptide. In some embodiments, the S2A lacks a signal peptide. 
     One of skill in the art will recognize that individual substitutions, deletions or additions to a peptide, or protein sequence which alters, adds, or deletes a single amino acid or a small percentage of amino acids in the encoded sequence is a conservatively modified variant where the alteration results in the substitution of an amino acid with a similar charge, size, and/or hydrophobicity characteristics, such as, for example, substitution of a glutamic acid (E) to aspartic acid (D). In some embodiments, the chimeric molecule comprises a mutation of N to D at position 88 of the IL-2 section of the molecule. In some embodiments, the chimeric molecule comprises SEQ ID NO: 14. In some embodiments, the chimeric molecule consists of SEQ ID NO: 14. In some embodiments, the chimeric molecule comprises SEQ ID NO: 15. In some embodiments, the chimeric molecule consists of SEQ ID NO: 15. In some embodiments, the chimeric molecule comprises SEQ ID NO: 16. In some embodiments, the chimeric molecule consists of SEQ ID NO: 16. In some embodiments, the chimeric molecule comprises SEQ ID NO: 17. In some embodiments, the chimeric molecule consists of SEQ ID NO: 17. In some embodiments, the chimeric molecule comprises a sequence selected from SEQ ID NO: 14, 15, 16, and 17. In some embodiments, the chimeric molecule consists of a sequence selected from SEQ ID NO: 14, 15, 16, and 17. In some embodiments, SEQ ID NO: 14-17 and SEQ ID NO: 4-7 respectively but comprising the N88D mutation. 
     In some embodiments, the peptide derived from NKp44 comprises a sequence derived from SEQ ID NO: 10, with one or more conservative substitution. According to another embodiment of the invention, the peptide derived from NKp44 comprises a sequence homologous to SEQ ID NO: 10. According to another embodiment of the invention, the peptide derived from NKp44 comprises a sequence having greater than 70%, 75%, 80%, 85%, 90% or 95% homology to SEQ ID NO: 10. Each possibility represents a separate embodiment of the present invention. 
     As used herein, the term “analog” includes any peptide having an amino acid sequence substantially identical to one of the sequences specifically shown herein in which one or more residues have been conservatively substituted with a functionally similar residue and which displays the abilities as described herein. Examples of conservative substitutions include the substitution of one non-polar (hydrophobic) residue such as isoleucine, valine, leucine or methionine for another, the substitution of one polar (hydrophilic) residue for another such as between arginine and lysine, between glutamine and asparagine, between glycine and serine, the substitution of one basic residue such as lysine, arginine or histidine for another, or the substitution of one acidic residue, such as aspartic acid or glutamic acid for another. Each possibility represents a separate embodiment of the present invention. 
     As used herein, the phrase “conservative substitution” also includes the use of a chemically derivatized residue in place of a non-derivatized residue provided that such peptide displays the requisite function such as iron precipitation as specified herein. 
     In another embodiment, the peptide derived from amino acids 130 to 199 of SEQ ID NO: 1 is a variant of native NKp44 or a fragment thereof, which differs by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 20 conservative amino acid substitutions from the amino acid 130-199 of native NKp44 (SEQ ID NO: 1) or a fragment thereof. Each possibility represents a separate embodiment of the present invention. In another embodiment, the peptide derived from NKp44 is a variant of the native NKp44 which differs by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 modifications from SEQ ID NO: 10. Each possibility represents a separate embodiment of the present invention. In another embodiment, the peptide derived from NKp44 is a variant of the native NKp44 which differs by at most 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 modifications from SEQ ID NO: 10. Each possibility represents a separate embodiment of the invention. 
     In one embodiment, the peptide derived from NKp44 is a variant of SEQ ID NO: 10 comprising or consisting of the amino acid sequence as set forth in SEQ ID NO: 11. SEQ ID NO: 11 is SPASASTQTSWTPRDLVSSQTQTQSCVPPTAGARQAPESPSTIPVPSHPSSPLPVPLP SRPQASTLRPGP. 
     In another embodiment, the term “variant” refers to a polypeptide or nucleotide sequence which comprises a modification of one or more amino acids or nucleotides as compared to another polypeptide or polynucleotide, respectively. In some embodiments, the modification are substitution, deletion, and/or insertion of one or more amino acids or nucleotides as compared to another polypeptide or polynucleotide, respectively. In some embodiments, the changes may be of minor nature, such as conservative amino acid substitutions or for nucleotide sequence resulting in conservative amino acid substitutions that do not significantly affect the activity of the polypeptide. In some embodiments, the changes may be substitution of an amino acid molecule, resulting in an addition of a glycosylation site (N- or O-linked), thereby increasing glycosylation of the polypeptide. 
     Typically, the present invention encompasses derivatives of the peptides. The term “derivative” or “chemical derivative” includes any chemical derivative of the peptide having one or more residues chemically derivatized by reaction of side chains or functional groups. Such derivatized molecules include, for example, those molecules in which free amino groups have been derivatized to form amine hydrochlorides, p-toluene sulfonyl groups, carbobenzoxy groups, t-butyloxycarbonyl groups, chloroacetyl groups or formyl groups. Free carboxyl groups may be derivatized to form salts, methyl and ethyl esters or other types of esters or hydrazides. Free hydroxyl groups may be derivatized to form O-acyl or O-alkyl derivatives. The imidazole nitrogen of histidine may be derivatized to form N-im-benzylhistidine. Also, included as chemical derivatives are those peptides, which contain one or more naturally occurring amino acid derivatives of the twenty standard amino acid residues. For example: 4-hydroxyproline may be substituted for proline; 5-hydroxylysine may be substituted for lysine; 3-methylhistidine may be substituted for histidine; homoserine may be substituted or serine; and ornithine may be substituted for lysine. 
     In addition, a peptide derivative can differ from the natural sequence of the peptides of the invention by chemical modifications including, but are not limited to, terminal-NH2 acylation, acetylation, or thioglycolic acid amidation, and by terminal-carboxlyamidation, e.g., with ammonia, methylamine, and the like. Peptides can be either linear, cyclic or branched and the like, which conformations can be achieved using methods well known in the art. 
     The peptide derivatives and analogs according to the principles of the present invention can also include side chain bond modifications, including but not limited to —CH2-NH—, —CH2-S—,-CH2-S=0, OC—NH—, —CH2-O—,-CH2-CH2-, S═C—NH—, and —CH═CH—, and backbone modifications such as modified peptide bonds. Peptide bonds (—CO—NH—) within the peptide can be substituted, for example, by N-methylated bonds (—N(CH3)—CO—); ester bonds (—C(R)H—C—O—O—C(R)H—N); ketomethylene bonds (—CO-CH2-); a-aza bonds (—NH—N(R)—CO—), wherein R is any alkyl group, e.g., methyl; carba bonds (˜CH2-NH—); hydroxyethylene bonds (—CH(OH)—CH2-); thioamide bonds (—CS—NH); olefmic double bonds (—CH═CH—); and peptide derivatives (—N(R)—CH2-CO—), wherein R is the “normal” side chain, naturally presented on the carbon atom. These modifications can occur at one or more of the bonds along the peptide chain and even at several (e.g., 2-3) at the same time. 
     The present invention also encompasses peptide derivatives and analogs in which free amino groups have been derivatized to form amine hydrochlorides, p-toluene sulfonylamino groups, carbobenzoxy amino groups, t-butyloxycarbonyl amino groups, chloroacetylamino groups or formylamino groups. Free carboxyl groups may be derivatized to form, for example, salts, methyl and ethyl esters or other types of esters or hydrazides. The imidazole nitrogen of histidine can be derivatized to form N-im-benzylhistidine. 
     As used herein the term “salts” refers to both salts of carboxyl groups and to acid addition salts of amino or guanido groups of the peptide molecule. Salts of carboxyl groups may be formed by means known in the art and include inorganic salts, for example sodium, calcium, ammonium, ferric or zinc salts, and the like, and salts with organic bases such as salts formed for example with amines such as triethanolamine, piperidine, procaine, and the like. Acid addition salts include, for example, salts with mineral acids such as, for example, acetic acid or oxalic acid. Salts describe here also ionic components added to the peptide solution to enhance hydrogel formation and/or mineralization of calcium minerals. 
     The peptide analogs can also contain non-natural amino acids. Examples of non-natural amino acids include, but are not limited to, sarcosine (Sar), norleucine, ornithine, citrulline, diaminobutyric acid, homoserine, isopropyl Lys, 3-( 2 ′-naphtyl)-Ala, nicotinyl Lys, amino isobutyric acid, and 3-( 3 ′-pyridyl-Ala). 
     Furthermore, the peptide analogs can contain other derivatized amino acid residues including, but not limited to, methylated amino acids, N-benzylated amino acids, O-benzylated amino acids, N-acetylated amino acids, O-acetylated amino acids, carbobenzoxy-substituted amino acids and the like. Specific examples include, but are not limited to, methyl-Ala (Me Ala), MeTyr, MeArg, MeGlu, MeVal, MeHis, N-acetyl-Lys, O-acetyl-Lys, carbobenzoxy-Lys, Tyr-O-Benzyl, Glu-O-Benzyl, Benzyl-His, Arg-Tosyl, t-butylglycine, t-butylalanine, phenylglycine, cyclohexylalanine, and the like. 
     The invention further includes peptide analogs, which can contain one or more D-isomer forms of the amino acids. Production of retro-inverso D-amino acid peptides where at least one amino acid and perhaps all amino acids are D-amino acids is well known in the art. When all of the amino acids in the peptide are D-amino acids, and the N- and C-terminals of the molecule are reversed, the result is a molecule having the same structural groups being at the same positions as in the L-amino acid form of the molecule. However, the molecule is more stable to proteolytic degradation and is therefore useful in many of the applications recited herein. Diastereomeric peptides may be highly advantageous over all L- or all D-amino acid peptides having the same amino acid sequence because of their higher water solubility, lower immunogenicity, and lower susceptibility to proteolytic degradation. The term “diastereomeric peptide” as used herein refers to a peptide comprising both L-amino acid residues and D-amino acid residues. The number and position of D-amino acid residues in a diastereomeric peptide of the preset invention may be variable so long as the peptide is capable of displaying the function of prolonging the half-life of the chimeric polypeptide. 
     In one embodiment, the peptide derived from NKp44, comprises an amino acid sequence selected from the group consisting of: SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 10, and SEQ ID NO: 11. In one embodiment, the peptide derived from NKp44, comprises an amino acid sequence selected from the group consisting of: SEQ ID NO: 2, and SEQ ID NO: 3. 
     In one embodiment, the peptide derived from NKp44 is glycosylated. In one embodiment, the sequence of the peptide derived from NKp44 comprises at least one glycosylation site, 2 glycosylation sites, 3 glycosylation sites, 4 glycosylation sites, 5 glycosylation sites, 6 glycosylation sites, 7 glycosylation sites, 8 glycosylation sites, 10 glycosylation sites, 11 glycosylation sites, 12 glycosylation sites or 13 glycosylation sites. In one embodiment, the glycosylation site is an “N-linked” glycosylation site and/or “0-linked” glycosylation site. 
     As used herein, an “N-linked” glycosylation site includes, without limitation, asparagine (Asn) followed by any of X-Serine, X-Threonine and X-Cysteine, wherein X is any amino acid except proline, and glycosylation occurs on the Asn residue. In this invention, the amino acid sequence of any polypeptide situated N-terminal to, C-terminal to, or in between two N-linked sites, can be of any content and length needed to suit a particular design requirement. As used herein, an “O-linked” glycosylation may occur at any serine or threonine residue with no single common core structure or consensus protein sequence. 
     By another aspect, there is provided a chimeric molecule comprising an amino acid sequence selected from the group consisting of SEQ ID NO: 14-18. 
     In some embodiments, the chimeric molecule is an IL-2 chimeric molecule. In some embodiments, the chimeric molecule consists of an amino acid sequence selected from the group consisting of SEQ ID NO: 14-18. In some embodiments, the chimeric molecule comprises SEQ ID NO: 14. In some embodiments, the chimeric molecule consists of SEQ ID NO: 14. In some embodiments, the chimeric molecule comprises SEQ ID NO: 15. In some embodiments, the chimeric molecule consists of SEQ ID NO: 15. In some embodiments, the chimeric molecule comprises SEQ ID NO: 16. In some embodiments, the chimeric molecule consists of SEQ ID NO: 16. In some embodiments, the chimeric molecule comprises SEQ ID NO: 17. In some embodiments, the chimeric molecule consists of SEQ ID NO: 17. 
     By another aspect, there is provided a pharmaceutical composition comprising the chimeric molecule of the invention. 
     In some embodiments, the pharmaceutical composition comprises a pharmaceutically acceptable carrier, excipient or adjuvant. In some embodiments, the composition is formulated for systemic administration. In some embodiments, the composition is formulated for local administration. In some embodiments, local is local inflammation. 
     By another aspect, there is provided a use of an IL-2 chimeric molecule characterized by increased serum half-life for increasing regulatory T cells (Tregs) in a subject. 
     By another aspect, there is provided an IL-2 chimeric molecule characterized by increased serum half-life for use in increasing regulatory T cells (Tregs) in a subject. 
     In some embodiments, the subject is a subject in need thereof. In some embodiments, the IL-2 chimeric molecule is a pharmaceutical composition comprising an IL-2 chimeric molecule. In some embodiments, the IL-2 chimeric molecule is a chimeric molecule of the invention. In some embodiments, the IL-2 chimeric molecule is a molecule such as described hereinabove. 
     As used herein, the term “about” when combined with a value refers to plus and minus 10% of the reference value. For example, a length of about 1000 nanometers (nm) refers to a length of 1000 nm+−100 nm. 
     It is noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a polynucleotide” includes a plurality of such polynucleotides and reference to “the polypeptide” includes reference to one or more polypeptides and equivalents thereof known to those skilled in the art, and so forth. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. 
     In those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. All combinations of the embodiments pertaining to the invention are specifically embraced by the present invention and are disclosed herein just as if each and every combination was individually and explicitly disclosed. In addition, all sub-combinations of the various embodiments and elements thereof are also specifically embraced by the present invention and are disclosed herein just as if each and every such sub-combination was individually and explicitly disclosed herein. 
     Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following examples, which are not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples. 
     Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples. 
     EXAMPLES 
     Generally, the nomenclature used herein and the laboratory procedures utilized in the present invention include molecular, biochemical, microbiological and recombinant DNA techniques. Such techniques are thoroughly explained in the literature. See, for example, “Molecular Cloning: A laboratory Manual” Sambrook et al., (1989); “Current Protocols in Molecular Biology” Volumes I-III Ausubel, R. M., ed. (1994); Ausubel et al., “Current Protocols in Molecular Biology”, John Wiley and Sons, Baltimore, Md. (1989); Perbal, “A Practical Guide to Molecular Cloning”, John Wiley &amp; Sons, New York (1988); Watson et al., “Recombinant DNA”, Scientific American Books, New York; Birren et al. (eds) “Genome Analysis: A Laboratory Manual Series”, Vols. 1-4, Cold Spring Harbor Laboratory Press, New York (1998); methodologies as set forth in U.S. Pat. Nos. 4,666,828; 4,683,202; 4,801,531; 5,192,659 and 5,272,057; “Cell Biology: A Laboratory Handbook”, Volumes I-III Cellis, J. E., ed. (1994); “Culture of Animal Cells—A Manual of Basic Technique” by Freshney, Wiley-Liss, N. Y. (1994), Third Edition; “Current Protocols in Immunology” Volumes I-III Coligan J. E., ed. (1994); Stites et al. (eds), “Basic and Clinical Immunology” (8th Edition), Appleton &amp; Lange, Norwalk, Conn. (1994); Mishell and Shiigi (eds), “Strategies for Protein Purification and Characterization—A Laboratory Course Manual” CSHL Press (1996); all of which are incorporated by reference. Other general references are provided throughout this document. 
     Materials and Methods: 
     Plasmid design: Protein sequences were designed and sent to Hylabs®, where a humanized DNA sequence was matched, and the cassette was inserted into a pCDNA-3.1(+) backbone. Sequence of the protein included an IL-2 signal peptide (MYRMQLLSCIALSLALVTNS, SEQ ID NO: 9), followed by a fragment of the NCR2 (Nkp-44) protein ( 34 AA; residues 130 to 163), the complete sequence of IL-2 ( 133 AA; residues 21 to 153) and a second NCR2 fragment ( 36 AA; residues 164 to 199) 45 . The sequence ends with an HRV 3C cleavage site followed by a 6XHis tag tail. Plasmids were transformed into DH1α bacteria and extracted after proliferation. 
     Protein Production and purification: Plasmids were transfected into HEK293F cells, which were cultured in shaking flasks. After three days, the supernatant was separated from cells using centrifugation and filtering. FPLC process was done using ÄKTA™ (GE Healthcare®), where supernatant was supplemented with 500 mM imidazole (Sigma-Aldrich®) solution in a ratio of 1:25 and loaded on a nickel-ion column (HisTrap™ GE Healthcare®). Elution performed with 500 mM imidazole solution. The washed fraction was concentrated and further cleaned in Amicon® (Millipore®) with 10 kDa cutoff. Sample concentration was measured using NanoDrop™ (ThermoFisher Scientific®), assuming the extinction coefficient calculated with ExPASy Protparam tool, according to protein sequence. Protein was then diluted to a level of 1 mg/mL, divided into small aliquots in Eppendorf Protein LoBind tubes, and frozen at −80° C. 
     SDS-PAGE: Five μg of protein solution was denaturized in β-mercaptoethanol and SDS solution at 95° C. for 5 minutes, before loading on SDS-PAGE 12% acrylamide gel, and ran at 100V. Protein was stained using InstantBlue™ (Expedeon®). 
     ELISA for binding assay: We used the Biolegend® ELISA MAX™ kit for the detection of human IL-2. For binding assay, purified S2A was compared to recombinant human IL-2, Aldesleukin (Peprotech, Cat no. 200-02). 96-well ELISA plates were coated with capture ab according to the protocol supplied with the kit, and then proteins were serially-diluted in the plate. Capture ab, HRP, and TMB were added according to the protocol supplied with the kit. Plates were read sequentially, at 650 nm without stop solution, and the best reading was chosen. Data were fitted to 4 parameters logistic (4PL) model, and EC 50  was extrapolated, using GraphPad® Prism™ 5.0. 
     MTT assay using CTLL-2 cells for Specific Activity evaluation: CTLL-2 cells were cultured in complete RPMI supplemented with 25 units/mL of recombinant human IL-2 (Proleukin® Novartis Pharma GmbH, Germany). In 96-well plates, serial dilutions of cytokines were carried out. CTLL-2 cells were then washed three times with PBS, and 1×10 4  cells were seeded per well in a 96 well plate, in a volume of media equal to the volume of media in the well, to a total of 90 μL, essentially halving the concentration of cytokines across all wells. Cells were incubated for two days, and on the third, 10 μL 5 mg/mL MTT (Sigma-Aldrich®) solution was added to each well. Cells were further incubated to allow metabolism of the MTT, and after 1-2 hours, formazan crystals were dissolved by adding 1004, per well of isopropanol (supplemented with 0.5% HCl) and pipetting. Plates were read at 570 nm, and 630 nm and results subtracted (630 nm from 570 nm) to obtain the normalized results, which were fitted to 4 parameters logistic (4PL) model and ED 50  was extrapolated, using GraphPad® Prism™ 5.0. Specific activity is calculated according to the formula: 
     
       
         
           
             
               Specific 
               ⁢ 
               
                   
               
               ⁢ 
               Activity 
               ⁢ 
               
                   
               
               ⁢ 
               
                 ( 
                 
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                   ⁢ 
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             = 
             
               
                 
                   1 
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                     10 
                     6 
                   
                 
                 
                   ED 
                   50 
                 
               
               ⁢ 
               
                   
               
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                   ng 
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     Preparation of cytokines for injection: The number of units available for each cytokine was determined according to CTLL-2 assay. Prior to the experiment, aliquots of cytokines were made with the required amount of units to be injected, taking into consideration a 28% loss due to two defrost cycles. The volume and dilution of aliquots were calculated to accommodate a 100 μL injection volume per mouse. Dilution was made in sterile PBS 1× solution (Hy-Labs®). Aliquots were then refrozen at −80° C. until injection time. The vehicle is PBS 1× solution. 
     Pharmacokinetics: Mice (5 mice per group) received subcutaneous (SC) injection of Proleukin (180 pmol, 8,000 units) and S2A ( 15  pmol, 30 pmol, and 60 pmol, that correspond to 3,000 units, 6,000 units and 12,000 units, respectively) at time 0. Blood samples (10 μL) were collected from the tail vein prior to the dosing, at 10 and 30 min, then at 1, 2, 4, 24, 30, 42, and 72 h. Alsever&#39;s solution (200 μL) was added to the samples to prevent coagulation, and they were stored at −80° C. pending analysis. Blood concentrations of Proleukin and S2A were measured using the Biolegend® ELISA MAX™ kit for the detection of human IL-2 based on appropriate calibration curves. Non-compartmental pharmacokinetic analysis of the observed concentration vs. time data was performed using the PKSolver 2.0 add-in for Microsoft® Excel™ 46  for each mouse separately and averaged by treatment post-analysis. 
     PBMCs isolation and FACS analysis: 200 μL blood was collected into a tube coated with EDTA to prevent clotting and immediately added to 1 mL Alsever&#39;s solution. RBCs were lysed in ACK buffer made in the lab. WBCs were counted, and 100,000 cells of each sample were transferred into a well of a 96-well plate where the subsequent procedure was done. Cells were blocked with anti-CD16/CD32 (Biolegend®, clone: 93), and membranal proteins were stained with anti-CD45 PE/Cy7 (Biolegend®, clone: 30-F11), anti-CD4 FITC (Biolegend®, clone: GK1.5), anti-CD8 Pacific Blue (Biolegend®, clone: 53-6.7), anti-CD25 PE (Biolegend®, clone: PC61), and anti-CD69 APC/Cy7 (Biolegend®, clone: H1.2F3). Cells were then fixed and permeabilized using the TruNuclear™ kit (Biolegend®) and stained with anti-FoxP3 APC (ThermoFisher Scientific®, clone: FJK-16s). Cells were than read in Beckman Coulter® Gallios™ flow cytometer. Results were gated and analyzed using Kaluza™ 2.1. 
     Immunohistochemistry: Tissue sections of 5 μm thickness were cut from FFPE blocks using a fully automated rotary microtome (Leica RM2255). Morphology of tissues was assessed using staining with hematoxylin (Mayer) and 1% alcoholic eosin (Pioneer research chemical Ltd, UK) staining. For IHC staining, tissue sections were serially deparaffinized with xylene ( 3  times for 5 mins) and then rehydrated with absolute ethanol ( 2  times for 5 mins). The endogenous peroxidase activity of sections was quenched with methanolic 3% H 2 O 2  solutions for 20 min. After washing with doubled distilled water, antigen retrieval was done at 95° C. using citrate buffer pH 6.0 (Zytomed) as an antigen unmasking solution. Sections were then washed, and ImmPRESS universal reagent (Vector Laboratories, MP-7500) was used according to the manufacturer&#39;s protocol for the blocking. After the blocking, sections were incubated overnight at 4° C. with primary antibody against FoxP3 (diluted 1:50, BioLegend, cat no—320001). Following extensive washings, sections were then incubated with HRP conjugated secondary antibody from ImmPRESS universal reagent (Vector Laboratories, MP-7500) for 30 minutes. Lastly, staining was visualized by using AEC solution (Zymed Laboratories, San Francisco, Calif., USA) according to manufacturer&#39;s protocol, the reaction stopped in the water, counterstained with hematoxylin and tissue sections were mounted with aqueous mounting medium (Vectamount™ AQ, cat no-H-5501). 
     Tissue images were scanned by a panoramic scanner and analysed by HistoQuant™ software ( 3 D Histech). For FoxP3 staining, the software calculated the number of positive nuclei and the annotated area for each tissue, and the value was expressed as object frequency (pcs/mm 2 ). 
     Naive model: C57b1/6 WT mice, 8 weeks old were obtained from Envigo® and injected with 30,000 IU of Proleukin, S2A and the same volume of PBS (day 0). At day 3 blood was drawn and PBMCs isolated for flow-cytometry (as described in the “PBMCs isolation and FACS analysis” subsection). A day later (day 4) mice were injected again in the same manner. At day 7, mice were sacrificed, and blood was drawn and PBMCs isolated for flow-cytometry. 
     Evan&#39;s Blue: On the day of sacrifice in the in vivo naive model for T cell induction, mice were injected intravenously with 100 μl 2% Evans blue solution freshly prepared in sterile PBS. The mice were allowed to recuperate and remain mobile for two h, after which, lungs were harvested, washed twice in PBS, and placed into tubes containing 2 mL Formamide and incubated at 37° C. for 24 h. After incubation, absorbance of the supernatant was measured at 650 nm and compared against Evans blue standard curve. 
     Metastatic melanoma model: B16-BL8 cells were cultured in complete RPMI. 8 weeks old C57b1/6 WT mice were obtained from Envigo® and acclimatized before experimentation. Before injection, cells were washed and suspended in serum-free RPMI medium. At day 0, each mouse was inoculated intravenously in the tail vein with 1×10 5  cells (in 100 μl media without any supplement). Mice were allowed 5 days for metastasis to develop in lungs before cytokine injection. Each mouse was injected with 30,000 units of respective cytokine dissolved in PBS 1× in a total volume of 100 μl per injection as described under “Preparation of cytokines for injection” heading. The vehicle was PBSx1. Injections were given subcutaneously every 4 th  day after 5 days of B16-BL8 inoculation. Blood samples were collected on day 18 (sacrifice). PBMC was stained and analyzed, as described above. On day 18, mice were sacrificed, lungs were harvested and weighed. Immunohistochemistry was performed on excised lungs, as described in the “Immunohistochemistry” section. 
     Colitis model: To induce colitis, 6 weeks old C57b1/6 WT mice obtained from Envigo® were given 2.5% Dextran Sulfate Sodium (DSS, TdB®) in the drinking water for one week (defined as DSS period). During this period, mice were injected twice with cytokines on day 2 and 6, counted from the onset of DSS administration. On day 8, half of the mice in each group were sacrificed. Blood was drawn and colon removed and measured for length. Samples from colons were fixed for IHC. The rest of the mice were allowed one week of recovery (plain water without DSS was given) before sacrificed in an identical manner on day 15. Mice were weighed every day throughout the experiment. Clinical manifestation of diarrhea and blood in stool were also tracked by touching a tissue paper to the mouse anus and examining the stain. Clinical scoring was done by factoring weight loss percentage with clinical manifestation (weight: 1-5% loss—1 point, 6-10% loss—2 points, 11-20% loss—3 points, more than 20%—4 points. Stool consistency: well formed—0 points, semi formed stool—2 points, liquid stool—4 points). Each mouse was injected with 30,000 units of respective cytokine dissolved in PBS 1× in a total volume of 100 μL per injection, as described in “Preparation of cytokines for injection” part. The vehicle was PBS 1×. PBMCs were stained and analyzed, as described above. IHC was scored by summing the parameters—depth of injury (none—0 points, mucosal and submucosal—2 points, transmural—3 points), crypt damage (none—0 points, basal one-third damaged—1 point, basal two-thirds damaged—2 points, only surface epithelium intact—3 points, entire crypt and epithelium lost—4 points), percentage of tissue involvement (1-25%—1 point, 26-50%—2 points, 51-75%—3 points, 76-100%—4 points), percentage of immune cell infiltration (1—25%—1 point, 26-50%—2 points, 51-75%—3 points, 76-100%—4 points). 
     Rheumatoid Arthritis model: These mice spontaneously develop rheumatoid arthritis as they age. For this experiment, mice were chosen before showing clinical signs, at the age of 3 weeks. Hind limb joints were then measured using a digital caliper, twice a week. Each mouse was injected with 100,000 units of respective cytokine dissolved in PBS in a total volume of 100 μL per injection as described in “Preparation of cytokines for injection” section, with PBS 1× as the vehicle. Injections were given every four days, for a total of 7 doses. On the 21st day, blood was sampled, and PBMCs were stained and analyzed as described above. 
     Statistics: Student&#39;s t-tests and Mann-Whitney U tests were performed using a python script utilizing the statistics module of the ‘SciPy’ library. Means, medians, confidence intervals, and folds were calculated using the ‘pandas’ library. ANOVAs were calculated in Statistica™. 
     Example 1: Modification of IL-2 with Sequences Derived from NKp44 
     Previously the inventors defined an amino acids sequences derived from the hinge region of NKp44 isoform 2 (NP_001186438.1, SEQ ID NO: 1) as capable of prolonging the biological half-life (T 1/2 ) of human growth hormone. These sequences included the SPA sequence (SEQ ID NO: 2; 34 amino acids from residues 130 to 163 of SEQ ID NO: 1) and APE sequence (SEQ ID NO: 3; 36 amino acids residues 164 to 199 of SEQ ID NO: 1) of NKp44 isoform 2, respectively. Therefore, these sequences were tested in combination with proteins exhibiting a very short in vivo half-life such as IL-2. A chimeric human IL-2 was produced as shown in  FIG. 1A  in which wild-type human IL-2 (NP_000577.2, SEQ ID NO: 13, residues 21 to 153 without the signal peptide) is flanked by the SPA sequence and the APE sequence at the N- and C-termini, respectively. This recombinant modified human IL-2 is termed S2A (SEQ ID NO: 4). The NKp44 hinge region is highly glycosylated, particularly with 0-glycans. The glycosylation of SPA and APE caused an apparent molecular weight of nearly 50 kDa for S2A ( FIG. 1B ), in contrast to the calculated molecular weight of 26 kDa based on the AA sequence of S2A. Next it was tested whether the SPA and APE modifications change the structure and in vitro function of the IL-2 component of S2A. A commercial sandwich ELISA was employed to test purified S2A and commercially available recombinant human IL-2, called Aldesleukin (Peprotech, Cat no. 200-02). The ELISA-based measured EC50 of Aldesleukin was 7.5 pg/ml, while the measured EC50 of S2A was 13.4 pg/ml ( FIG. 1C ). This difference may be experimental error, due to the effect of glycosylation on extinction coefficient or from an effect of the SPA and APE additions on the structure of the IL-2 component in the S2A as recognized by the capture and detector anti IL-2 antibodies in this commercial sandwich ELISA. 
     The ELISA results showed that the effect of the SPA and APE modifications on the structure of the IL-2 was negligible. Next, the in vitro functional effect of this modification was tested. The CTLL-2 assay is the standard assay to calculate the specific activity of IL-2 measured in IU/mg. The CTLL-2 assay was thus employed to compare the in vitro function of S2A and the Aldesleukin drug employed in the clinic (Proleukin®). The CTLL-2 assay measured on average a mean effective dose (ED50) of Peoleukin as 340 pg/ml, while the measured ED50 of S2A was 135 pg/ml, nearly half ( FIG. 1D ). This difference could not be attributed to the experimental error range of the specific experiment. A summary of 5 different CTLL-2 experiments comparing S2A and Proleukin, shows that fold change in ED50 between S2A and Proleukin is indeed near half ( FIG. 1E ), meaning that S2A has higher IUs per mg protein as compared to the Proleukin and is thus more effective at stimulating proliferation of CTLL-2 cells. Similar results were found for S2S, A2A and A2S, as they also were found to be superior to Proleukin. 
     Example 2: Pharmacokinetic Analysis of S2A and Proleukin 
     To compare the PK of S2A and Proleukin following subcutaneous (SC) inoculation, groups of mice (n=5) were injected once with a dose of S2A or Proleukin. The doses were either 3000 IU (15 pmol), 6000 IU (30 pmol), or 12000 IU (60 pmol) for S2A or 8000 IU (180 pmol) for Proleukin. Blood was first taken at time “0 min” and proteins were then injected SC. At all subsequent time points, blood samples were taken without additional injections of the proteins. Blood was diluted and kept frozen. Following the end of the experiment, samples were defrosted, analyzed by ELISA and pmol/ml blood were calculated.  FIG. 2A  shows the calculated PK curves. The area under the curve (AUC), representing the bioavailability of the drug (the fraction of the drug that was absorbed and reached the systemic circulation), was 5.8, 8.5 and 15.2 pmol/ml*min for the 3 different doses of S2A. In contrast, the AUC value for Proleukin was considerably lower ( 2 . 86 ) even though the inoculated dose was 180 pmol (8,000 IU) as compared to the 15, 30 and 60 pmol (3,000, 6,000 and 12,000 IU) for the S2A doses. In accordance with these observations, the clearance half-life (T1/2 clearance) of the S2A was calculated to be near 1,000 min (1,084, 937 and 1123 minutes for the 3 doses respectively) while the T1/2 clearance of Proleukin was significantly lower (35 minutes). In contrast to the sharp differences in values of AUC and T1/2 clearance, the Cmax values of S2A and Proleukin, representing the maximum drug concentration observed in the blood, were very similar. An inoculation dose of 60 pmol (12,000 IU) S2A resulted in a 0.009 pmol/ml (1.77 IU/ml) Cmax; while a dose of 180 pmol (8000 IU) Proleukin resulted in 0.022 pmol/ml (0.99 IU/ml) Cmax. Interestingly, the time to reach the Cmax (Tmax) was substantially faster for the Proleukin (48 vs 156 min for 12,000 IU S2A), indicating that Proleukin is absorbed to the blood faster than the S2A, thus making S2A effectively a slow release molecule. Similar results were observed for two other IL-2 chimeric molecules S2S and A2A ( FIG. 2B ). 
     Example 3: S2A Inoculation Induced Substantial Levels of T reg    
     Mice were inoculated twice with 30,000 units of S2A, Proleukin and vehicle on days 0 and 4 and the phenotype of blood PBMCs on days 3 and 7 were assessed. The following lineage and activation markers were stained for: CD45, CD4, CD8, CD25, FoxP3 and CD69 ( FIG. 3A ). Proleukin and S2A treatments did not mediate a substantial change in the CD4 +  fraction of the CD45 +  PBMC as compared to vehicle. The CD8 +  fraction of the CD45 +  PBMC was slightly induced by S2A treatment at day 3 ( FIG. 3B ), although this effect was not statistically significant and not observed at day 7 ( FIG. 3C ). However, when the cells were stained for the CD25 marker, a different pattern was observed; S2A, but not Proleukin, treatment manifested a significant induction (5.6-fold as compared to vehicle) of the CD4 + CD25 +  subset in the CD45 +  PBMC ( FIG. 3B-3C , significant at day 7). This enhancement was more evident on day 7 following the two inoculations of S2A ( FIG. 3C ). The fraction of the CD8 + CD25 +  subset in the CD45 +  cells was negligible. When the cells were stained for the classic T reg  phenotype (CD4 + CD25 + FoxP3 +  subset within the CD4 +  cells), the effect of S2A treatment was even more prominent, becoming increasingly clear on day 7, with a 6.1-fold enhancement in T regs  observed ( FIG. 3B-3C ). Proleukin treatment induced negligible amounts of classical T reg  as compared to Vehicle. For CD8 +  cells, the amount of CD25 + FoxP3 +  cells was negligible and similar between Proleukin and S2A. Finally, the fraction of CD25+CD69+ activated T cells was assessed. The fraction of the CD25+CD69+ subsets in the CD4 +  and CD8 + PBMC cells of the S2A-treated mice was negligible as compared to the considerably enhanced fraction of CD25 + FoxP3 +  cells in the CD4 +  population. To summarize, treatment with S2A, but not with Proleukin, induced a prominent expansion of the classical T reg  phenotype; this prominent effect was not observed for the CD25+CD69+ phenotype either in the CD8 + or CD4 +  cells, indicating a lack of T cell activation. 
     Example 4: S2A Inoculation Enhance B-16 Growth and Frequency of T reg  within the TME 
     Mice (n=5 per treatment) were injected with 100,000 cells of the melanotic cell-line—B16BL8, and metastasis were allowed to form in the lungs for the next 6 days, at which point the mice were inoculated with 30,000 units of S2A, Proleukin and an equivalent volume of vehicle. Mice were inoculated repeatedly every 4 days. At the 4th day after the last injection, mice were sacrificed, and lungs were removed. All lungs, regardless of treatment exhibited melanotic nodules on the surface of the lungs ( FIG. 4A ). To assess the mass of tumors in the lungs, the lungs were weighed. It was found that the lungs removed from mice treated with S2A were significantly heavier than lungs removed from mice treated with Proleukin or vehicle (1.3-folds and 1.5-fold respectively) ( FIG. 4B ) indicating increased cancer spread. Immunohistological staining for FoxP3 was performed on the lungs to evaluate the tumor micro-environment and histology of the nodules ( FIG. 4C ). The object frequency of FoxP3 positive cells was scanned and calculated and it was found that lungs removed from the S2A group showed significantly higher frequency (10 folds) of these cells as compare to Proleukin and vehicle ( FIG. 4D ). In addition, PBMCs extracted at the day of sacrifice were stained in a similar manner to that described supra and it was found that S2A inoculated mice showed a significant decrease in the CD4 +  and CD8 +  subsets of the CD45 +  population (0.6 folds and 0.58 folds respectively) ( FIG. 4E ). At the same time, the CD4 + CD25 +  and CD8 + CD25 +  subsets were induced significantly (5.3 folds each) as compare to vehicle ( FIG. 4E ). Further, the CD4 + CD25 + FoxP3 +  subset was also significantly increased (5.3 folds) as compared to vehicle and Proleukin, as was the CD8 + CD25 + FoxP3 +  subset (8.2 folds). In absolute terms as considered as part of the CD8 +  population this increase was lower than the respective percentage increase out of the CD4 +  population (Classical T Regs ). Induction of the CD4 + CD25 + CD69 +  subset of the CD4 +  population and the CD8 + CD25 + CD69 +  subset of the CD8 +  population was negligible ( FIG. 4E ). This indicates that the S2A indeed produces an immunosuppressive environment, and thus is unsuitable for cancer therapy. 
     Example 5: Treatment with S2A Reduced the Development of DSS-Induced Colitis 
     To test the ability of S2A to induce immunosuppression in a pathological setting, colitis was induced in mice by adding DSS to their drinking water. Mice were then inoculated with 30,000 units S2A, Proleukin or an equivalent volume of vehicle, at day 3 of the DSS period and day 6 of the DSS period. The DSS period lasted a week, after which mice had a one-week recovery period without DSS. At the end of the DSS period half of the mice in each group were sacrificed, and their colons removed and measured. The remaining mice were sacrificed after the recovery period, and their colons removed and measured ( FIG. 5A ). It was found that mice inoculated with S2A were more resistant to colitis than the Proleukin group and vehicle group. Colon length of the S2A group, was significantly longer at the end of the DSS period as compare to the vehicle group, and longer (but not statistically significantly) as compare to the Proleukin group ( FIG. 5B , left). After the recovery period, the difference in colon length was significant both as compared to the vehicle and the Proleukin group ( FIG. 5B , right). 
     Mice weights and clinical signs (diarrhea and anal bleeding) were tracked throughout the experiment ( FIG. 5C-5D ). Weight loss as a percentage of the initial weight was calculated and was found to be significantly different in a two-way ANOVA test (p-value &lt;0.0005), when taking into consideration the effect of both time and treatment ( FIG. 5C ). The effect of treatment alone was also significant (p-value &lt;0.0005), and in post-hoc tests, weight loss in the S2A group was found to be significantly different from that in the Proleukin group (p-value &lt;0.05) and the vehicle group (p-value &lt;0.0005). Clinical signs were factored with weight loss to compile a clinical score. In a two-way ANOVA test a significant difference in the clinical score (p-value &lt;0.0005) attributed to the combined effect of treatment and time was found, as well as a significant difference due only to the component of treatment (p-value &lt;0.0005) ( FIG. 5D ). In a post-hoc test, a significant difference in the clinical score was found between the S2A group and the vehicle group, but not between S2A and Proleukin. Nonetheless, when only the recovery period was considered, a statistically significant difference was evident between the S2A group and the Proleukin group (p-value &lt;0.005). 
     At the end of the DSS period as well as at the end of the recovery period PBMC populations were analyzed. While no relative induction of the CD4+ sub-population of the CD45+ population was apparent at the end of the DSS period (day 8), and the CD4+CD25+ sub-populations were almost negligible as a percentage of the CD45+ population in all groups, the CD4+CD25+FoxP3+(classical T Reg ) subset of the CD4+ population was significantly induced in the S2A treated mice as compared to both vehicle and Proleukin (2.7-fold and 1.3-folds respectively) ( FIG. 5E ). The CD8 + CD25+FoxP3 subset was somewhat induced in the S2A group but not significantly at the end of the DSS period ( FIG. 5E ). No significant induction of the CD4 + CD25 + CD69 +  or CD8 + CD25 + CD69 +  subsets was measured at the end of the DSS period. At the end of the recovery period (day 16, and day 10 since last inoculation) no significant difference was apparent in any population in any treatment ( FIG. 5F ). 
     Example 6: Treatment with S2A Reduced the Induction of Rheumatoid Arthritis (RA) 
     The effect of S2A in a second pathological setting was also tested. IL-1 receptor antagonist knockout (IL-1ra KO) mice spontaneously develop rheumatoid arthritis (RA) 3-6 weeks after birth, as a result of an inability to counterbalance the pro-inflammatory effect of IL-1. The question of whether S2A inoculation could attenuate the severity and progression of RA compared to Proleukin was investigated. Mice at the age of 4 weeks (n=5) were inoculated with 100,000 units of S2A, Proleukin or a corresponding volume of vehicle. Inoculation began at day 2, and was preformed every 3 days, for a total of 7 inoculations. As expected, signs of RA soon manifested in the form of inflammation and swelling of the hind-limb joints ( FIG. 6A ). Joint widths were measured throughout the experiment. Two-way ANOVA preformed on the data normalized to the vehicle treated group found that while the combined effect of time and treatment was not significant, the treatment component alone was significant (p-value &lt;0.0005) ( FIG. 6B ). PBMCs were isolated on day 21 (3 days after 5th inoculation) of the experiment. A significant induction of the CD4 + CD25 +  subset of CD45 +  cells in the S2A group was measured on day 21 as compare to the vehicle group (6.4 folds, p-value &lt;0.05). And while it was not statistically significant, a small induction was also seen as compared to the Proleukin group (1.8 folds) ( FIG. 6C ). In the CD8 + CD25 +  subtype similar inductions were also seen; however, these were not statistically significant. The classical T Reg  phenotype (CD4 + CD25+FoxP3 + ), showed a significant induction in the S2A group as compared to the vehicle group (2.1 folds, p-value &lt;0.005), and a smaller and non-significant induction as compare to Proleukin (1.3 folds). CD8 + CD25+FoxP3 +  levels were negligible in all treatment groups. 
     Example 7: S2A is Superior to the N88D IL-2 Mutant 
     Having established the superiority of the S2A molecule as compared to wild-type IL-2 (Proleukin), the molecule was next compared to a known IL-2 mutant N88D. The N88D mutant has been shown to have reduced binding to the IL-2Rβγ receptor, and to induce T reg  expansion. The N88K mutation is also known to have the same effect. A similar experiment was performed to the one in Example 2, however in this instance S2A was compared to N88D. 
     Mice were inoculated twice with 25,000 or 50,000 international units (IU) of N88D, 25,000, 50,000 or 100,000 IU of S2A and vehicle on days 0 and 4 and the phenotype of blood PBMCs on days 3 and 7 were assessed. Total CD4 and CD8 cells were not altered at day 3 or 7 regardless of the treatment ( FIG. 7A ). However, examination of the CD25 positive subset showed that both S2A and N88D enhanced this population of cells, however, S2A was significantly superior as compared to N88D both at day 3 and day 7 ( FIG. 7B ). An enhancement of CD8 positive CD25 cells was also observed, although this subset was minor in compared to the CD4 population and the increase was caused only by S2A and not N88D. Most notably, the T reg  phenotype of CD4/CD25/FoxP3 was greatly enhanced by S2A and to a lesser extent by N88D ( FIG. 7C ). This difference was most pronounced at day 3 but was still significant at day 7. The CD8/CD25/FoxP3 subset was negligible at both days and with all treatments. 
     Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.