Process for the selective extracorporeal separation of blood constituents

The invention relates to processes and apparatus employing filter candles with an effective filter surface area of 0.2 to 2 square meters and a mean pore diameter of 0.2 to 2 micron in sterilizable cylindrical housings for the selective extracorporeal separation of precipitates of macromolecular pathologic and/or toxic species from blood or blood constituents, such as whole serum or plasma.

The invention relates to a method and apparatus, employing a filter candle, 
for the selective extracorporeal separation of pathologic and/or toxic 
blood constituents. 
Progress made in recent years in the field of analysis of the lipoprotein 
system of the human body has shown that a high plasma cholesterol 
concentration, and hence the risk of early arteriosclerosis, specifically 
coronary sclerosis, is attributable essentially to the presence of high 
concentrations of high-cholesterol beta-lipoproteins in the body. In human 
blood normally about 70 to 80% of the total cholesterol is bound to 
beta-lipoproteins (low density lipoproteins, referred to as LDL). In 
morbid processes which are accompanied by a disturbed lipo-metabolism or 
respectively elevated plasma lipid concentrations, the percentage of 
LDL-combined cholesterol in the total cholesterol may rise even higher. As 
a rule, therefore, hypercholesterolemia is brought about by 
hyper-beta-lipoproteinemia. 
Therapeutic efforts to effectively lower the beta-lipoprotein 
concentrations have heretofore been unsatisfactory Especially in the 
genetic forms of lipo-metabollic disorders, control by medication is 
extremely difficult. 
Two methods have been tried heretofore, for mechanically separating 
beta-lipoproteins from blood: elimination of LDL from blood by means of 
specific antibodies that are coupled to a matrix; and complete exchange of 
the entire blood serum by plasmapheresis. 
The antibodies used for the first method were obtained by immunizing sheep 
or rabbits. This method (W. Stoffel and Th. Demant, Selective Removal of 
Apolipoprotein B-Containing Serum Lipoproteins from Blood Plasma, Proc. 
Nat. Acad. Sci., U.S.A., 78, 611-615 (1981)) has the disadvantage of low 
efficiency, which has already led to a modification of the treatment 
procedure by this method. In addition, there is danger, theoretically, 
that the use of antibodies produced in an animal might in the long run 
cause immunological problems in the person being treated. 
In plasmapheresis, which involves a complete exchange of the entire blood 
serum, the beta-lipoprotein content of the affected patient is indeed 
lowered, but under the conventional methods, due to their particular 
instrumentation, those lipoproteins (i.e., high density lipoproteins, HDL) 
which counteract arteriosclerosis are also eliminated concurrently. 
Moreover, all other proteins of the plasma, including coagulation factors, 
globulins and hormones, are eliminated as well. However, until now, this 
method has proved useful for very specific cases of 
hyper-beta-lipoproteinemia. 
In order to remove beta-lipoproteins from the blood or blood plasma 
selectively and at high capacity, the corpuscular constituents of the 
blood are separated by known methods, for instance, as described in 
co-pending U.S. patent application Ser. No. 414,809, filed Sept. 3, 1982, 
and the remaining plasma is mixed with heparin in a suitable buffer, e.g., 
an acetate-citrate buffer, the beta-lipoprotein-heparin complex which 
thereafter forms being precipitated at the isoelectric point at a pH of 
5.05 to 5.25 and subsequently removed. 
Numerous other diseases are also accompanied by a rise in the content of 
antibodies or of macromolecular species of a pathogenic nature, the 
concentrations of which also have been lowered successfully by 
plasmapheresis. To this end, the toxic species are removed selectively by 
precipitation. Examples of such species are globulins, such as the 
rheumatic factor, Bence-Jones factors and also other pathogenic 
macromolecules. 
Several methods have been described for the separation of such high 
molecular weight species from blood plasma. Thus, Swiss patent No. 626,256 
discloses an apparatus for the continuous extracorporeal separation of 
such substances from the blood. This apparatus consists of a filtering 
device containing a medium which adsorbs the macromolecular species. The 
adsorber contains insolubilized enzymes, antigens or antibodies, but it is 
incapable of selective separation of certain species present along with 
related ones also existing in the plasma, especially under 
non-physiological conditions as they occur in cryoprecipitation or after 
denaturation by heat. 
Filtration methods using membrane or capillary filters have been described, 
e.g., in European Patent EP-A No. 0,041,350. In a so-called filtration 
cascade, the plasma which contains the macromolecules is separated from 
the blood in a first filtering stage, and then, in a second filtration 
stage, the macromolecules are removed therefrom at a physiological 
temperature or under cooling. The nominal pore diameter of the second 
membrane is stated to be 0.01 to 0.2 micron. 
The disadvantage of such membrane and capillary filters is that, for the 
separation of larger quantities of precipitates, their surfaces are too 
small and, for reasons of membrane stability, their pore diameters are too 
small. In addition, such filters clog very quickly with the precipitates 
and with entrained fibrin, especially if the filtration takes place under 
pressure. This often necessitates a filter change in the extracorporeal 
circulation system, with all the medical and technical complications 
incident thereto. 
The invention described herein has as an objective a process and apparatus 
which permit removing pathologic and/or toxic species of relatively high 
molecular weight from the blood, i.e., from whole serum or from 
constituents of the blood such as plasma, selectively and with a high 
capacity, in an extracorporeal circulation system. Here filters should be 
used which, after selection of a suitable and widely variable pore width, 
completely retain relatively large quantities of precipitates from a large 
quantity of plasma, offer little resistance to the plasma, and do not clog 
in the course of the filtration process. 
The objective is achieved by the use of filter candles in a process and 
apparatus suitable for the separation of the named species. 
The invention relates to a process for the selective, extracorporeal 
separation of precipitates, such as are produced by addition of 
precipitation agents and/or chemical reagents or denaturation by cooling 
or heating, of macromolecular pathologic and/or or toxic species from 
blood or blood constituents such as whole serum or plasma. 
Characteristically, it employs a plasma fraction which has been produced 
by a capillary or membrane plasma filter or the last filter of a cascade 
of several such filters with molecular exclusion limits of 50,000 to 
3,000,000 Dalton continuously from patient blood or fractions thereof, and 
which plasma fraction contains precipitates of macromolecular pathologic 
or toxic species produced by addition of precipitation agents and/or 
chemical reagents or by denaturation by cooling or heating. The process 
comprises passing such a plasma fraction at atmospheric pressure through a 
cylindrical sterilized housing comprising a filter candle, the filter 
candle having a filtration means and an inner core, and being installed in 
a closed extracorporeal circulation system, whereby such plasma fraction 
sweeps the filtration means externally and whereby plasma purified by 
filtering passes into the interior core and the precipitates are retained 
in or on the filtration means; discharging the purified plasma from the 
core; and returning purified plasma to a patient. 
The invention also relates to apparatus for the selective extracorporeal 
separation of precipitates of macromolecular pathologic or toxic species 
from blood or blood constituents. The apparatus comprises a filter candle 
having an effective filter surface in the range of from about 0.2 to about 
2 square meters, a mean pore diameter in the range of from about 0.2 to 
about 2 micron, the filter candle also having an internal core, and being 
disposed in a sterilizable cyclindrical housing made of plastic or glass. 
The housing is provided with at least one filtrate outlet adapted to 
permit drainage of fluid filtrate from the core, and with a first inlet 
located at one end of the housing and adapted to permit introduction of 
blood or a fraction thereof. Such first inlet is located between the outer 
radius of the core and the inner radius of the housing. 
In a further embodiment, the invention comprises, in a process for the 
selective extracorporeal separation of precipitates of macromolecular 
pathologic and/or toxic species from blood or blood constituents, such as 
whole serum or plasma, the improvement of employing a filter candle having 
an effective filter surface in the range of from about 0.2 to about 2 
square meters, a length in the range of from about 10 to about 60 cm, and 
a mean pore diameter in the range of from about 0.2 to about 2 micron, 
disposed in a sterilizable cylindrical housing. 
The filter candles employed in practicing the invention are commonly used 
in technical filtration processes, e.g., in the purification of drinking 
water and the production of ultra-pure water for special purposes. They 
have a mean pore diameter in the range from about 0.2 to about 2 micron, 
preferably in the range from about 0.4 to about 1 micron, which enables 
them on the one hand to completely retain the precipitated pathologic 
and/or toxic species as precipitates, while on the other hand offering 
virtually no resistance to the plasma. 
The effective filter surface of the filter candles used is in the range 
from about 0.2 to about 2 square meters, preferably in the range of from 
about 0.8 to about 1.7 square meters, depending on the length of the 
filter candles used, which typically is in the range of from about 10 to 
about 60 cm. The filter candle should be of the same length as the housing 
in which it is disposed. Such large surfaces are found to be suitable for 
absorbing, without clogging, the entire precipitates from 2 liters of 
plasma, which is a typical quantity of a purification run in a patient. 
According to the invention, all filter candles which meet the requirements 
referred to herein may be employed. A specific filter candle which has 
been employed is sold under the trademark NUCLEPORE QR, the filtration 
medium of which consists of a polycarbonate membrane.

The apparatus of the invention for the selective extracorporeal separation 
of the precipitates from blood or blood plasma, which can be installed as 
a filter section in a cascade filtration system, consists of a cylindrical 
housing 1, which may be fabricated of plastic or glass, and which is, as 
depicted, threaded at its upper and lower ends. At the upper and lower 
ends, the cylinder is closed by internally threaded covers 2, which by 
means of ultrasonic welding may be hermetically and sterilely sealed. The 
cylindrical housing 1 contains a filter candle having an interior core 3 
and a filter body 4. The covers 2 are provided with filtrate outlets 6, 8. 
As depicted, outlet 6 is adapted for the withdrawal of the filtrate, i.e., 
the plasma which has been filtered, and outlet 8 is capped. Typically, 
filtrate outlets 6, 8 are co-axial with core 3, but this is not essential. 
One cover 2 is provided with a first inlet 5, adapted for the introduction 
of the plasma fraction to be filtered. The other cover is provided with an 
outlet 7, adapted for the withdrawal of excess plasma and suspended 
solids. Inlet 5 and outlet 7 are located between the outer radius of core 
3 and the inner radius of housing 1. Core 3 and filter body 4 should 
exactly match the interior volume of the housing as to dimensions, and 
should be glued tightly into the housing 1 in such a way that the core 3 
lies between filtrate outlets 6, 8, while the filter body 4 lies at the 
levels of inlet 5 and outlet 7. 
Referring now to FIG. 2, which depicts apparatus especially adapted for 
cryoprecipitation or heat denaturation, housing 1 is surrounded by a 
thermostatically-controlled jacket 9, through which any desired cooling or 
heating fluid can be conducted via inlet and outlet ports 10. 
Referring now to FIG. 3, housing 1 may be heated by means of heating wires 
12, to achieve denaturation by heat constituents contained in the plasma. 
Current is supplied to the heating wires 12 via two plug contacts 11 which 
are disposed to permit, just like mounting coupling 13, direct electrical 
plugging of the filter housing 1 into, for example, a monitor. 
The filter candles and the apparatus described according to the invention, 
as well as the connections to the remainder of the circulation system for 
extracorporeal separation of precipitates from blood or blood plasma, are 
designed so as to permit working under sterile conditions, which is 
imperative in such cases. This requires that all materials be selected so 
as to permit sterilization under the usual conditions. 
An essential advantage of the process of the invention over the methods 
known in the prior art is that, by comparison with capillary filters, no 
lateral drain nipple at the cylinder jacket for withdrawing the purified 
plasma by means of a vacuum is necessary. Due to the structural design of 
the filter candles, the plasma supplied through inlet 5 sweeps the filter 
surface of filter candle 4 externally. The filtrate penetrates into the 
interior core 3 by gravity alone, without application of an external 
vacuum, and is conducted away via outlet 6. The precipitate remains in the 
fabric of the filter. That portion of the plasma which is not filtered off 
by gravity can be removed via outlet 7, and, if desired, may be 
recirculated by combining it with fresh plasma being introduced via outlet 
5. Outlet 8 then remains closed. Thus, the process operates at the ambient 
atmospheric pressure, without the need for applying a pressure 
differential across the filtration means. 
If, for instance to remove the rheumatic factor, the plasma is to be cooled 
to a low temperature during cryoprecipitation in order to achieve 
precipitation of the species to be separated, a suitable 
temperature-controlling liquid, preferably water, may be introduced via 
inlet port 10 into the thermostatically-controlled jacket 9, as shown in 
FIG. 2, with the result that the plasma is cooled to a temperature preset 
by a thermostat. The filtered plasma, which is withdrawn via outlet 6, 
must then be warmed to body temperature again before being returned into 
the patient's blood circulation. 
For the separation of blood plasma constituents precipitated by heat 
denaturation, e.g., Bence-Jones factors, the apparatus of FIG. 3 may be 
employed. Current is supplied to the heating wires 12 via plug contacts 
11; the temperature can be controlled exactly by means of a regulating 
system (not shown). The purified plasma withdrawn through outlet 6 must be 
cooled accordingly to body temperature before being returned into the 
patient circulation. 
The further advantages of the method of the invention therefore reside in 
that, depending on the specific requirements of the particular separating 
process, very specific, controlled conditions can be set and maintained, 
without giving up the other advantages of the method, namely an almost 
pressureless filtration via filter systems with a very large surface 
without danger of obstruction of the filters and all the complications 
connected therewith. 
The invention is exemplified by the following examples. 
EXAMPLE 1 
The blood of a patient with hereditary hypercholesterolemia (homozygote) 
with a starting cholesterol value of 416 mg/dl or, respectively, an LDL 
cholesterol value of 368 mg/dl, was to be purified from beta-lipoproteins. 
There was used a simple cylinder housing according to FIG. 1 which 
contained a filter candle of a mean pore diameter of 0.4 micron, sold 
under the trademark NUCLEPORE QR. 
Two liters of the patient's blood plasma were diluted in the volumetric 
ratio 1:1 with 2 liters of 0.2 M sodium acetate buffer (pH: 4.86) which 
contained 50,000 units per liter of heparin, which resulted a pH value of 
the mixture of 5.12. 
The heparin-buffer-plasma mixture was subjected to the method of the 
present invention, whereby the plasma was completely purified from 
low-density lipoproteins within 30 minutes. 
Despite this concentration of LDL, found only in rare cases, and the volume 
of plasma, there was no observed pressure increase at the filter. The 
filter remained clear to the end. At no time did the clear filtrate 
contain low-density lipoproteins. 
EXAMPLE 2 
In accordance with Example 1, plasma from patient blood which contained the 
rheumatic factor and "C.sub.1q binding immune complexes" was subjected to 
cryoprecipitation. To this end, the plasma was introduced into apparatus 
constructed according to FIG. 2, the thermostatically-controlled jacket 
having been cooled to 4.degree. C. The filter candle had a mean pore 
diameter of 0.4 micron, sold under the trademark NUCLEPORE QR. After 
filtration, the purified plasma contained less than 5% of the originally 
present rheumatic factors and "C.sub.1q binding immune complexes" 
EXAMPLE 3 
The separation of Bence-Jones factors from blood plasma was conducted after 
denaturation by heating to 50.degree. C. in apparatus constructed 
according to FIG. 2, the thermostatically-controlled jacket of which had 
been heated to 50.degree. C. The filter candle had a mean pore diameter of 
0.4 micron, sold under the trademark NUCLEPORE QR. After filtration, the 
plasma was free from denaturation products. No obstruction of the filter 
was observed. 
EXAMPLE 4 
The separation of Bence-Jones factors from blood plasma was conducted after 
denaturation by heating to 50.degree. C. in apparatus constructed 
according to FIG. 3. The filter candle had a mean pore diameter of 0.4 
micron, sold under the trademark NUCLEPORE QR. 
After filtration, the plasma was free from denaturation products. No 
obstruction of the filters was observed 
While the processes and apparatus described herein constitute preferred 
embodiments of the invention, it is to be understood that there are 
variations in materials and equipment which may be employed which included 
in the invention as define by the appended claims. Therefore, the detailed 
description should be considered illustrative rather than as restrictive.