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Human sera were tested for cytotoxicity to pairs of long-term tissue-cultured cell lines. Each pair had been derived from the same individual and one of the pairs possessed the characteristics of either "T" or "B" cells. The alloantisera used were HL-A-typing reagents or sera obtained from Amish multiparas. Selected cytotoxicity was found against the B-cell lines by direct testing. Cytotoxicity was abolished by absorption with B-cell line but not by absorption with the T-cell lines. The results suggest that a group of allotypic antigens may be expressed exculsively on human B cells.

Sera, previously found to react specifically with B lymphoid cultured cells, were tested on isolated T and B peripheral blood lymphocytes in a microcytotoxicity assay. Studies were performed on lymphocytes obtained from several large Amish families. The sera used in these studies were cytotoxic to peripheral blood, B lymphocytes, but not cytotoxic to T lymphocytes. The antigens detected followed the inheritance pattern of HL-A haplotypes. The strong linkage disequilibrium with HL-A antigens suggests that genes controlling the expression of B lymphocyte antigens are linked to genes controlling HL-A alloantigens.

In a sibship of 5 brothers and 7 sisters, 3 sisters died from acute myelocytic leukaemia while a 4th probably had the same disease. Laboratory studies on the close relatives revealed that a 5th sister had persistently high erythrocyte sedimentation-rates and serum-IgM levels and serological evidence of acute leukaemia-associated antigens. These findings suggest a possible preleukaemic state in this patient.

Patients in remission with advanced acute lymphatic leukemia were randomly assigned to receive chemotherapy alone or chemotherapy plus immunotherapy with a Burkitt lymphoma tissue culture cell line (RAJI). Remission duration in both groups were identical. Complement-dependent cytotoxic antibody was seen in 5 of 8 immunized patients and 0 of 8 controls. This antibody reacted with RAJI and both allogeneic and autologous acute leukemia cells. Antibody titers began to rise after 2 months, peaked at 4 months, and then declined prior to relapse in all patients. The time course of the increase in mixed-leukocyte culture response to RAJI was similar to immunized patients. An increased in vitro response to phytohemagglutinin was seen during drug administration in all patients. Although no clinical benefit was seen in this small number of patients with the RAJI injections, these in vitro responses are encouraging and new immunization schedules will be investigated.

HL-A antigens having specificities HL-A2, HL-A7, HL-A12 have been solubilized by papain treatment of membrane preparations from the cultured human lymphoblastoid cell line RPMI 4265 and purified about 80-fold by chromatography on carboxymethylcellulose, Sephadex G-150, and diethylaminoethylcellulose columns. Separation of HL-A2 from a mixture of HL-A7 and HL-A12 was achieved on the final DEAE-cellulose column. The yield was about 1 mg of protein of each antigen preparation per 100 g of packed, frozen cells. On sodium dodecyl sulfate gel electrophoresis both preparations showed two polypeptide bands. The smaller subunit of 12,000 daltons is common to all HL-A preparations and has been shown to be identical with beta2-microglobulin. The larger subunit is a glycopeptide and in the HL-A7, 12 preparation was resolved into a duplex of 34,000 and 37,000 daltons. The HL-A2 preparation showed a single band at 34,000 daltons. On isoelectric focusing under nondenaturing conditions, the preparation showed multiple bands, all of which contained both subunits and retained antigenic activity. On isoelectric focusing in the presence of 6 M urea a single band for beta2-microglobulin and multiple bands for the larger subunit were seen. This charge heterogeneity of the larger subunit has been shown to be due to variable amounts of sialic acid. When HL-A antigen preparations were subjected to Sephadex G-100 chromatography in the presence of 3 M KCl, no separation of the two subunits was observed.

Leukemia patients in remission were immunized with RAJI lymphoid tissue culture cell lines. Four of 7 patients developed antibody to the immunizing cell as well as to allogeneic leukemia cells. Sera from 3 patients were tested against autochthonous tumor cells either frozen or obtained at the time of disease relapse. Patient's sera were cytotoxic to their own leukemia cells; however, this cytotoxicity was lost at the time of relapse.

Two human sera having both complement-dependent and lymphocyte-dependent antibody activities (CDA, LDA) were applied to isoelectrofocusing columns. Maximum LDA activity for both sera was found focused at a higher pH than maximum CDA activity. The studies suggest that LDA molecules may exist without having complement-dependent activity.

A water-soluble component of membranes of cells from a Burkitt's lymphoma cultured cell line was used to develop an antiserum that detects an antigen(s) on acute leukemia cells. This antiserum did not react with nonlymphoid cultured cell lines except for human embryonic kidney cells infected with the Rauscher murine leukemia virus. Absorption studies demonstrated this antigen to be crossreactive with the antigen detected on the human acute leukemia cells.

Antiserums to a purified cell membrane component from a Burkitt's lymphoma tissue culture cell line were produced in rabbits. These antiserums were cytotoxic to peripheral white blood cells from 8 of 15 patients with acute leukemia and 5 of 41 relatives, but not to peripheral white blood cells from leukemia patients in clinical remission or from normal individuals. These antiserums appear to be detecting an acute leukemia associated antigen or antigens.

Soluble preparations of HL-A alloantigens were separated by gel filtration into components having either the "LA" series or the "4" series of alloantigenic determinants. This separation may indicate that several different structural cistrons within the HL-A (locus) control the expression of these two series of determinants. The alternative possibility, in which one structural cistron with multiple mutational sites controls the synthesis of a single molecule cannot be excluded.

The molecular and chemical characteristics of membrane components bearing the major transplantation antigen systems in mouse (H-2) and man (HL-A) were compared and found to be strikingly similar. Kinetics of papain solubilization from cell membranes, gel filtration, and electrophoretic patterns of the alloantigenic components were found to be nearly identical. Comparable size heterogeneity of the solubilized materials was also demonstrated. Some differences in amino acid and carbohydrate content of the purified H-2 and HL-A alloantigenic materials were found. The general pattern of distribution of the amino acid residues, however, appears to be quite similar and indicate compositional relatedness in these materials. These physical and chemical similarities in the characteristics of molecules bearing the transplantation antigens are in accord with biologic studies indicating a comparable functional immunologic role for the mouse H-2 and human HL-A antigen systems. These studies support the view that the genes determining these major transplantation antigen systems may have evolved from a common precursor.