Specific killing of tumor cells in vitro in the presence of normal lymphoid cells and sera from hosts immune to the tumor antigens

Antibody-dependent cell-mediated cytotoxicity in serum samples from patients with ulcerative colitis. Relationship to disease activity and response to total colectomy

A group of six medically treated patients with ulcerative colitis were followed for up to 30 months along with eight additional patients who underwent proctocolectomy. Patients were examined frequently, and serum samples were collected for antibody-dependent cell-mediated cytotoxicity studies. Clinically active disease was substantiated by history, physical examination, laboratory investigations, proctoscopy and, when feasible, by rectal and/or colonic biopsy specimens. During active clinical disease, serum samples from patients with ulcerative colitis showed antibody-dependent cell-mediated cytotoxicity of 16.5 +/- 1.6 percent (range 8.2 to 25.8 percent). During remission of the disease, serum samples from the same patients demonstrated a mean antibody-dependent cell-mediated cytotoxicity value of 5.9 +/- 1.3 percent (range 0.4 to 11.1 percent) (p less than 0.01). In the eight patients who underwent proctocolectomy, mean preoperative antibody-dependent cell-mediated cytotoxicity value was 19.5 +/- 2.3 percent (range 4.1 to 38.6 percent). One month after proctocolectomy, antibody-dependent cell-mediated cytotoxic activity decreased by 72 +/- 11 percent of the preoperative value (p less than 0.001). These findings reveal a positive correlation between the antibody-dependent cell-mediated cytotoxicity with RPMI-4788 and clinical activity of ulcerative colitis, and support the hypothesis that the antibody being studied has direct relation to the presence of the ulcerative colitis colon in situ.

Enhanced K-cell activity in the peripheral blood of patients with malignant disease

We have analysed the influence of human malignant, inflammatory and infectious disease on the capacity of peripheral lymphocytes to mediate antibody-dependent haemolysis. The application of an enzyme-like kinetic model for measurement of maximal cytotoxic function has permitted reproducible and sensitive determinations of the K-cell function. The results show that malignant disease is associated with enhancement of ADCC capacity.

Effects of mitogens on ADCC activity and Fc receptor bearing cells

Murine spleen cells, when activated by various mitogens (Con A, PHA, LPS, BCG) or Con-A conditioned medium show altered behavior as effector cells of antibody-mediated cell cytotoxicity (ADCC) which does not correlate with the expression of Fc-receptors (FcR) at the effector cell surface.

Lymphocyte-dependent antibodies to antigen 3.1, a cell-surface antigen expressed by a subgroup of human melanomas

Previous work from our laboratory has led to the isolation of a monoclonal IgG2a mouse antibody, 3.2, which is specific for an antigen, 3.1, that is strongest expressed by a group of human melanomas. We have no demonstrated that this antibody can mediate antibody-dependent cellular cytotoxicity (ADCC) to human melanoma cells expressing antigen 3., and that lymphocytes from human peripheral blood can be used as the source of K cells. A monoclonal IgG1 antibody, 3.1, to the same determinant of antigen 3.1 gave only weak and inconsistent ADCC.

ADCC effector function in patients with atopic dermatitis. A possible mechanism of susceptibility to severe cutaneous viral infections

Peripheral blood mononuclear cells from patients with chronic atopic dermatitis were evaluated as effectors of antibody-dependent cellular cytotoxicity (ADCC) to determine if faulty effector function might explain the susceptibility of atopics to severe cutaneous viral infections in spite of adequate specific antibody titers. Eleven atopic patients whose dermatitis was well controlled and who were not infected or on immunosuppressive therapy were studied using sensitized human and chicken erythrocyte targets at three different effector:target ratios. No significant differences in mean ADCC were seen between atopics and controls. However, the function of peripheral blood mononuclear cells from atopic patients who had a previous history of severe cutaneous viral infection was significantly depressed against sensitized chicken, but not human targets. This suggests that atopic patients who develop severe cutaneous viral infections may represent a subset of atopics with an intrinsic or variable defect in K lymphocyte--mediated ADCC which might render them susceptible to persistent, extensive viral infections.

Antibody dependent cell-mediated cytotoxicity to herpes simplex virus in man: the influence of drugs on polymorphonuclear leucocyte and mononuclear effector cells

We have shown that the function of the effector cells in antibody mediated cell dependent cytotoxicity (ADCC) can be reduced by the use of a number of drugs and prostaglandins. Both polymorphonuclear leucocyte and mononuclear effector cells were studied. Aminophylline and isoproterenol markedly reduced this activity. All the prostaglandins tested--PGA1, A2, E1 and E2 had a similar but more profound effect. At a dose of 100 mg/ml hydrocortisone had relatively little influence and neither ASA nor indomethacin had any effect on the effector cells tested. It is suggested that the effect of PGE1 in stimulating a recrudescent herpes simplex infection may be by reducing the efficacy of ADCC in host defence.

Enhancement of tumor outgrowth by tumor-associated blocking factors

Transplanted lines of 3-methylcholanthrene (MCA)-induced BALB/c sarcomas were used for experiments in which tumors were mechanically suspended in Waymouth's culture medium, the suspensions centrifuged and filtered and the remaining cell-free "tumor fluids" (TF) tested for activity in vitro and in vivo. TF were found to inhibit ("block") cell-mediated cytotoxicity to tumor target cells in vitro with specificity for each tumor tested and even at high dilutions (1:1,000-1:10,000). In vivo, TF enhances the outgrowth of subcutaneously transplanted tumors in non-immune syngeneic mice. This enhancement had both specific and non-specific components, with the non-specific component being most apparent. Enhancement was best demonstrated when the TF were inoculated together with the tumor inocula. In one of two experiments in which TF were given intraperitoneally, specific enhancement was seen, whereas in the other, inhibition of tumor outgrowth was observed.

Human monocyte antibody-dependent cell-mediated cytotoxicity to tumor cells

Previous investigations of mononuclear cell antibody-dependent cell-mediated cytotoxicity (ADCC) toward tumor cells suggest that K lymphocytes and not monocytes are active in this cytotoxic reaction. This report, however, demonstrates that human monocytes are able to carry out ADCC toward three different human tumor cell lines (CEM T lymphoblasts, Raji bone marrow-derived (B) lymphoblasts, and HeLa cells). The cytolytic event was found to be temperature dependent and rapid, with most of the lysis occurring in the first 4 h of incubation. The extent of lysis was directly related to the number of monocytes (effector cells) and to the degree of antibody sensitization of the target cells. The antibody-dependent cell contact-mediated nature of the cytolytic event was confirmed by inhibition with competing nonspecific monomeric immunoglobulin and by the ability of monocytes in "innocent bystander" experiments to lyse antibody-coated targets but not nonantibody-coated target cells. Evidence that monocytes were clearly the effector cells in the monocyte preparations included the observation that preincubation of effector cells with opsonized zymosan particles abolished ADCC by monocytes, but had little effect on lymphocyte ADCC. Furthermore, no evidence for Fc receptor K lymphocyte contamination of the monocyte preparations was found using antibody-coated target cells that were selectively lysed by lymphocytes but not monocytes. We suggest that ADCC toward tumor cell targets may prove to be a useful assay of monocyte function in normal and disease states.

In vitro cytotoxicity of peritoneal macrophages activated with Mycobacterium smegmatis

Incorporation of 3H-TdR into EL4 leukemic cells in vitro was inhibited by peritoneal exudate cells (PEC) harvested from syngeneic C57BL/6J mice given an intraperitoneal (i.p.) injection of 1x10(7) viable Mycobacterium smegmatis ATCC 607 (Smeg) 4 days before. This phenomenon was also observed in the following five systems of PEC from animals and syngeneic tumor cells: C57BL/6J mice and B16 melanoma; DBA/2 mice and P815 mastocytoma; SWM/Ms mice and K5 fibrosarcoma; BALB/c, nu/nu mice and KKN-1 fibrosarcoma; and strain 2 guinea pigs and line-10 hepatoma. The in vitro cytotoxicity of the PEC activated by viable Smeg was much higher than those activated by dead-Smeg, viable BCG or proteose peptone. The activity of the adherent fraction of the PEC was stronger than that of the nonadherent one, and not influenced by either anti-theta or anti-mouse lymphocyte rabbit sera. The PEC induced with Smeg 4 days before contained a large population of mononuclear cells (88.9%) and a significant level of polymorphonuclear cells (PMN) (3.2%), and showed a much higher cytotoxicity than the PEC induced with Smeg 3 hr before, which contained a much larger population of PMN (71.9%), suggesting that PMN were not the effector cells in this system. In vitro and in vivo treatment with macrophage-inhibitors such as carrageenan, trypan blue and cytochalacin B, reduced the activity of the PEC. All of these facts suggested macrophages as the effector. Viable macrophages were required for the growth inhibition of EL4 in vitro: gamma-ray irradiated or freeze-thawed macrophages were ineffective. Kinetic studies revealed that inhibition of 3H-TdR incorporation into EL4 cells started within 3 hr of incubation together with the activated macrophages at an effector to target (E/T) ratio of 5, and the incorporation decreased gradually with the lapse of incubation time. On the other hand, 51Cr release from labelled EL4 was undetected when the E/T ratio was 5 but detected at on E/T of 10 or more. Even at the higher E/T ratio, at least 10 hr were needed until the release of 51Cr, suggesting that the activated macrophages produced growth inhibition of tumor cells followed by cell destruction.

Antibody-dependent cellular cytotoxicity in primary immunodeficiency diseases and with normal leukocyte subpopulations. Importance of the type of target

To gain insight into a possible role for antibody-dependent cell-mediated cytotoxicity in vivo, we examined the ability of leukocytes from 28 patients with primary immunodeficiency and from 20 normal controls to lyse three different types of antibody-coated targets in vitro. Mean cytotoxic indices +/-1 SD elicited by unfractionated mononuclear cells from normal controls were 28.74+/-13.26 for human HLA antibody-coated lymphocyte targets, 42.79+/-8.27 for rabbit IgG antibody-coated chicken erythrocyte targets, and 47.58+/-10.34 for human anti-CD (Ripley)-coated O+ erythrocyte targets. Significantly (P=<0.05) lower than normal mean cytotoxic indices against lymphocyte targets were seen with effector cells from 10 patients with X-linked agammaglobulinemia (3.7+/-4.33), in 10 with common variable agammaglobulinemia (16.05+/-7.74), in 3 with immunodeficiency with hyper IgM (18.41+/-4.88), and in 2 with severe combined immunodeficiency (3.94+/-0.3). Antibody-dependent cytotoxicity against chicken erythrocytes was significantly (P=<0.05) lower than normal only in the common variable agammaglobulinemic group (33.33+/-12.3) and against human erythrocytes only in the common variable (34.36+/-9.59) and hyper IgM (27.54+/-0.66) groups. Rosette and anti-F(ab')(2) depletion studies with normal leukocytes indicated that a nonadherent, nonphagocytic, non-Ig-bearing, non-C receptor-bearing, Fc receptor-bearing lymphocyte was the only effector capable of lysing HLA antiboyd-coated lymphocyte targets. Patients with infantile X-linked agammaglobulinemia and severe combined immunodeficiency appear to have a marked deficiency in this type of effector cell function.

Avian retrovirus-induced surface antigens and their cross-reactivity with chemically-transformed cells and primary embryonic cells of Japanese quails

By testing spleen cells from avian leukosis (ALV) and avian sarcoma virus (ASV)-injected Japanese quails in a microcytotoxicity assay against various target cells, we have demonstrated the existence of several target antigens. With non-transformed ALV-infected Japanese quail cells used as target cells, an avian retrovirus subgroup-specific destruction was obtained when spleen cells from animals infected with either avaian sarcoma or leukosis virus of the same subgroup were employed. This reaction is probably due to the virus envelope glycoproteins (Ve-gp) expressed on the cell surface. Apart from this subgroup-specific reaction, avian retrovirus group-specific destruction of ASV-transformed cells was demonstrated by means of effector cells immunized with ASV of a different subgroup. This reaction is restricted to transformed cells and not due to the virus envelope glycoprotein because the same effector cells are not cytotoxic to ALV-infected non-transformed cells but cytotoxic to sarcoma-virus-transformed cells which lack Ve-gp. Quail methylcholanthrene-tumor cells which show a transformation phenotype similar to that of ASV-transformed cells but which are free of detectable endogenous and exogenous retrovirus were also destroyed by the spleen cells from ASV tumorbearing animals. The same effector cells also exerted a weak cytotoxic effect on uninfected primary embryo cells but not to embryo cells after several passages.

Antibody-dependent cell-mediated cytotoxicity in the Moloney sarcoma virus system: differential activity of IgG and IgM with different subpopulations of lymphocytes

Antibody-dependent cell-mediated cytotoxicity in the Moloney sarcoma virus (MSV) system was evaluated in terms of the differential ability of IgG and IgM from MSV regressor animals to induce cytotoxicity by lymphocytes from lymph node, spleen, and thymus. The cell-mediated cytotoxicity induced by both IgM and IgG was specific for target possessing the appropriate virally determined cell surface antigen(s). IgM induced cytotoxicity by lymphocytes from all the organs tested. However, differences in magnitude and efficiency were revealed. Lymph node cells and thymocytes were most efficient against IgM-coated target cells. Against IgG-sensitized target cells, spleen and lymph node cells were about equally active, but thymocytes were inactive. Cortisone treatment of the donors of effector cells revealed that the cortisone resistant subpopulation of thymocytes, 2 days after cortisone injection, exhibited an increased cytotoxicity against target cells treated with unfractionated antiserum and its IgM fraction. This subpopulation of thymocytes was also cytotoxic against IgG-coated target cells. At 12 days after cortisone injection, the repopulated thymus showed little change in activity, compared to control thymus, against antibody-coated target cells.

Inhibitory effects of xenogeneic antiserum on the growth of Moloney virus-induced sarcomas

An antiserum was developed in rabbits by injections of a virus concentrate from Moloney murine sarcomas. Passive transfer of this antiserum attenuated the growth of both primary and transplanted Moloney murine sarcomas. It also facilitated tumor regression and increased survival times of young mice with primary Moloney sarcomas.

Antigens on melanoma cells detected by leukocyte dependent antibody assays of human melanoma antisera

Antibody-dependent cell-mediated cytotoxic assays have been used to examine antigens on human melanoma cells obtained either directly from patients or from long-term melanoma cell lines. A panel of melanoma antisera was selected from human subjects which could be shown not to have significant reactivity to histocompatibility antigens. With these antisera extensive cross-reactions between melanoma cells were found. However, the cross-reactivity was incomplete and the pattern of reactivity was different for each antiserum tested. These results were not consistent with a common melanoma antigen on human melanoma cells but rather indicated heterogeneity of melanoma antigens and multiple antibody specificities in the sera tested. This appeared to be confirmed by extensive cross-absorption studies which indicated limited cross-reactivity of antigens on melanoma cells from either long-term or short-term cultures. Several changes in the antigenic profile of melanoma cells in vitro from both long-term and short-term cultures were documented which resulted from contamination of the melanoma cell lines with non-melanoma cells and fibroblasts. Melanoma antisera may therefore be useful to mintor changes in long-term cultures which would otherwise give spurious results in in vitro tests. These results appear to have considerable significance for understanding tumour/host relationships and for the establishment of rational immunotherapeutic procedures and diagnostic tests in melanoma.

Cell-mediated immunity to mouse tumors: some recent findings

Lymphocyte mediated immune reactions play a major role in the immunological defense against antigenic tumor cells. Serum factors (antigens, antigen-antibody complexes) can thwart these reactions, perhaps by interfering with a lymphocyte "activation" process. Blocking factors can be eluted from lymphoid cells harvested from tumor-bearing animals. One way of increasing cell-mediated reactivity to tumor antigens appears to be to sensitize (or "activate") lymphocytes against tumor antigens in vitro. Another way may be to inoculate animals with sera containing lymphocyte-dependent and unblocking antibodies. Preliminary evidence is presented that inoculation of such sera from rabbits immunized with mouse embryonie cells and extensively absorbed may delay the appearance of primary, methyleholanthrene-induced sarcomas in BALB/c mice; the mechanisms responsible for this delay remain unknown.

Production of tumor-specific inducer of cellular cytotoxicity by lethally irradiated mice

Antisera taken 1 or 2 days after inoculation of BALB/c mice with transplantable sarcoma cells or Moloney sarcoma virus (MSV) induce tumor-specific cell-dependent cytotoxicity in vitro. In the present experiments, lethally irradiated ("immunosuppressed") mice were tested for the early appearance of the serum factor responsible for this anti-serum-dependent cell-mediated cytotoxicity (E-ADC). BALB/c mice were infected with MSV, syngeneic sarcoma cells or sheep red blood cells 24 h following irradiation with 900 R. Sera were obtained from MSV and tumor cell recipients 48 or 72 h later and tested for E-ADC activity. Spleen cells from SRBC recipients were tested at day 4 or 5 for ability to form direct plaques in a modified Jerne plague assay. Although the anti-SRBC response was obliterated in the irradiated mice, the E-ADC response appeared to be unimpaired. These studies indicate that newly synthesized immunoglobulin is not required for the formation of the E-ADC factor.

Antibody-dependent cell-mediated cytotoxicity in cows: comparison of effector cell activity against heterologous erthrocyte and herpesvirus-infected bovine target cells

Bovine peripheral blood leukocytes (PBL) and cells collected from the bovine mammary gland were assayed for antibody-dependent cell-mediated cytotoxicity (ADCC) against chicken erythrocyte (CRBC) and bovine herpesvirus-infected bovine kidney cell targets. Bovine antisera were used to sensitize target cells. Both PBL and mammary leukocytes expressed ADCC, with the latter cell population having greater activity against both target cells. Only the CRBC target cells were killed by nonadherent PBL and phagocyte-depleted PBL. Nonadherent mammary leukocytes, rich in monocytes and macrophages, did kill virus-infected target cells. Carbonyl iron-treated mammary leukocytes failed to kill virus-infected targets but could destroy CRBC targets. Antimacrophage serum inhibited lysis of both CRBC and virus-infected targets, but antilymphocyte serum only inhibited CRBC killing. These observations indicated that at least two kinds of cells could mediate ADCC against CRBC but only cells of the mononuclear phagocytic series could kill virus-infected target cells. The herpesvirus-infected target cells became susceptible to ADCC 9 h after virus infection. A case is made for investigating the phenomenon of ADCC using in vitro systems that closely mimic the in vivo situation. The possible role of the ADCC mechanism as instrumental in causing recovery from herpesvirus infections is discussed.

Human tumor cells grown in fetal calf serum and human serum: influences on the tests for lymphocyte cytotoxicity, serum blocking and serum arming effects

Peripheral blood lymphoid cells (PBL) from cancer patients and normal donors were tested against three melanoma cell lines grown in either 10% fetal calf serum (FCS) or 2.5-5% human AB serum in order to determine if the heterologous membrane (HM) antigen or other FCS antigens acquired from the bovine serum supplement could influence lymphoid cell-mediated cytotoxicity in vitro. FCS-grown melanoma cells were more susceptible than the AB serum-grown subline to lymphocyte cytotoxic effects. Arming effects by autologous sera on normal donor lymphocytes and to a lesser extent on lymphocytes of cancer patients were more pronounced on the FCS-grown M12 melanoma cells. This effect was abrogated when the cells were grown in human AB serum for at least 8 weeks. The non-HM tumor-associated antigen remained at the same original low level. Blocking effects were more evident on the AB-grown M14 melanoma line. These data suggest that the FCS antigens on the cell surface may have been responsible for the augmented PBL cytotoxicity. The anti-FCS antibody present in normal and cancer patients' blood induced an antibody-dependent cellular cytotoxicity (ADCC). Elimination of arming activity against HM or other FCS antigens from AB-grown cells may have made the serum blocking factors more apparent. However, cytotoxicity against tumor cells by PBL from normal donors was still apparent even on the human serum-grown cells, suggesting that a different antigen-antibody system was also responsible for this "non-specific" activity.

Kinetics of serum factors mediating blocking, unblocking and antibody-dependent cellular cytotoxicity in hamsters given isografts of para-7 tumor cells

Sera collected at intervals after PARA-7 tumor-cell inoculation were monitored for blocking, unblocking, and antibody-dependent cellular cytotoxicity (ADCC) using the microcytotoxicity test. Within 7 days after isografting, significant levels of blocking were demonstrated. This activity increased in parallel with tumor growth and reached a maximum at day 21. In contrast, the capacity of the sera to mediate ADCC was maximal at day 7, and no longer detectable at 3 weeks. Unblocking was not demonstrable in tumor-bearer sera. Further studies showed that, when the tumor was exicised, blocking activity fell rapidly while ADCC was elevated. Sera collected 7 days after surgery could neutralize the blocking activity of tumor-bearer sera. Significant levels of unblocking were still evident 10 weeks after surgery while ADCC had generally disappeared after 5 weeks. These findings illustrate the complexity of the hamster's humoral immune response to tumor cells, and suggest that (1) the sequestering of antibody by circulating tumor antigen accounts for the demise of ADCC in tumor-bearer sera and the concomitant appearance of blocking activity; and (2) the serum factors mediating ADCC and unblocking differ.

Characterization of cytotoxic spleen cells and effects of serum factors in a syngeneic rat tumour system

Splenocytes from inbred Wistar rats bearing a syngeneic squamous cell carcinoma (Spl) were fractionated by several techniques to characterize the lymphoid cells cytotoxic to the tumour in vitro. The anti-tumour cytotoxicity is presumably mediated primarily by T lymphocytes because it was greatly reduced by removal of T lymphocytes with heterologous anti-T serum plus complement but not by removal of other cell types. Cytotoxicity could be blocked at the tumour cell but not at the effector cell by sera taken late in tumour growth. Sera taken earlier in tumour growth could induce cytolysis of tumour cells by normal splenocytes but only if the tumour cells were treated with serum and washed before addition of the effector cells. Although splenocytes from normal and tumour-bearing rats were equally effective at lysing antibody-coated target cells it is unlikely that this mechanism is important in vivo as sera from early in tumour growth onwards contained factors (immune complexes?) which inhibited antibody-induced lymphocytolysis.

Lymphocytotoxicity to tumor target cells and interference of serum factors or tumor antigen with lymphocytotoxicity in patients suffering from different stages of breast carcinoma

The in vitro cytotoxicity of lymphocytes from patients suffering from breast carcinoma against autochthonous, allogeneic and established breast carcinoma cells was evaluated. Lymphocytotoxicity to breast carcinoma cells was observed in all stages of the disease. Control lymphocytes from healthy donors or patients suffering from other carcinoma are not cytotoxic for the breast carcinoma cell lines. A follow-up study of the cell mediated immune reactions before and after surgical removal of the breast carcinoma showed that the cytotoxic lymphocyte population which is demonstrated in the presence of the tumor disappears quickly after excision of the carcinoma. The non-reactivity of lymphocytes is not due to a general immune defect. Serum of the tumor bearers did not block the lymphocytotoxicity in early stage breast carcinoma; in metastatic disease inhibition occurred in more than half of the cases. Preincubation of lymphocytes with antigen preparations of allogeneic breast carcinoma cells did not inhibit the cytotoxicity to breast carcinoma cells whereas autologous serum preincubated with the antigen preparation diminished the lymphocyte reactivity to the target cells in some cases.

Temporal analysis of cellular cytotoxicity and humoral factors during progession and regression of Rous sarcomas in Japanese quails

Temporal appearance of cellular cytotoxicity and humoral activities including blocking and arming activities during the entire course of Rous sarcoma development in Japanese quails was examined by microcytotoxicity assay with comparison of animals bearing regressing tumors induced by a moderate dose of virus (regressors) and animals bearing growing tumors induced by a large dose of virus (progressors). Cellular cytotoxicity of the spleen cells in regressors was detected in a biphasic pattern; the first phase being observed as early as 3-5 days post inoculation (p.i.), followed by an eclipse period between 7-10 days p.i. which was the time of active tumor growth, and the second phase occurring after 12 days p.i. when the tumor had attained the maximum size. In progressors, only the first phase was observed. Instead, a stimulatory effect of the spleen cells on growth of target cells was noticed. Arming activity which confers cytotoxic activity on the normal spleen cells was demonstrated in the sera of regressors in the similar biphasic pattern as the cellular cytotoxicity; the early activity being present at 3 days p.i., and the late one after 19 days p.i. The former was detected by pre-incubation of serum with effector cells in microcytotoxicity assay and the latter by pre-incubation with target cells. In progressors, only the early arming activity which reacts with effector cells was demonstrated. Blocking activity which abrogates cellular cytotoxicity was demonstrated in both regressors and progressors but in different patterns of appearance, that is, blocking activity in regressors was only transiently demonstrated only by pre-incubation with effector cells at the time of maximum tumor growth, while the activity in progressors seemed to persist after the tumor reached the maximum size. Since the earlier activity was found to be effective at effector cell level, and the later one at both effector and target cell levels, participation of blocking factors of different types in progressors was also suggested.

Studies on the role of the host immune response in recovery from Friend virus leukemia. I. Antiviral and antileukemia cell antibodies

The humoral immune response to Friend virus leukemia was studied in congenic F1 mice differing in their incidence of recovery from leukemia. Antiviral neutralizing antibodies rose in titer in vivo concurrently with disappearance of viremia and fall in spleen virus levels. Cytotoxic antileukemia cell antibodies also appeared at this time. Passive transfer of these antibodies could inactivate low numbers of leukemia cells in vivo; however, mice of both high and low recovery genotypes produced antibodies in equal titer and recovered from viral infection in spite of striking differences in recovery from leukemic splenomegaly. Mice lacking C57BL genes did not produce antibodies or recover from viremia except in rare instances. Recovery from splenomegaly was found to be influenced by three or more C57BL genes independent of the H-2 complex.

Burkitt's lymphoma - a human tumor model system for immunological studies

Burkitt's lymphoma occurs mainly in parts of tropical Africa and has attracted the attention of experimental workers due to its epidemiological and clinical features, which indicate a viral etiology and a host immune response to the tumor. As a result of virological studies, Epstein-Barr virus (EBV) DNA has been demonstrated in almost all tested biopsies of African BL. This contrasts to the absence of EBV in all, or almost all, of the non-African Burkitt's lymphoma-like tumors, even though the number of tested tumors in this group is small, and to the lack of EBV in all other types of lymphoma or leukemia. Immunological studies have revealed the presence of antibodies to different EBV-associated antigens in all African patients with Burkitt's lymphoma. However the antibodies are not specific for Burkitt's lymphoma but are found in most adults all over the world, although at lower levels. They cannot therefore serve diagnostic purposes, but they can give prognostic information and occasionally give clues to the mechanisms behind late tumor recurrences, and possibly guide so-called immunotherapy. Burkitt's lymphoma patients contrast to appropriate control groups where some of the persons are anti-EBV seronegative, and this, together with the presence of EBV in Burkitt's lymphoma biopsies and the absence of EBV in other lymphomas, even though the cell type involved may be infectable by EBV in vitro and the tumor may arise in an EBV-carrying person, favors an etiological role in EBV in Burkitt's lymphoma and speaks against the "passenger" hypothesis, according to which EBV is picked up by the Burkitt's lymphoma cell which happens to be particularly suitable for EBV persistence. To explain the geographical distribution, a cofactor, such as certain forms of malaria, has been implied.

In vitro synthesis of tumor-specific factors with blocking and antibody-dependent cellular cytotoxicity (ADC) activities

Spleen cells from BALB/c mice bearing syngeneic sarcomas and from BALB/c mice whose sarcomas had been excised were cultivated in vitro. The culture supernatants were tested for two activities: their ability (1) to supress ("block") specific lymph-node cell-mediated cytotoxic reactions directed against the respective neoplasms; and (2) to induce antibody-dependent cellular cytotoxicity (ADC) specific for the antigens of the respective tumors. Both specific activities, blocking and induction of ADC, were detected in culture supernatants from spleens of tumor-bearing mice, even when repeatedly harvested at intervals over a 7-day period. Supernatants of cultured spleen cells from mice whose sarcomas had been excised 3-4 weeks previously also had ADC but no blocking activity. Supernatnats of cultures treated with inhibitors of protein synthesis lacked both blocking and ADC activities; the inhibitory effect of cycloheximide on these activities, as well as on protein synthesis, was reversible. Factors in the culture supernatants responsible for blocking and for ADC were labelled when the culture were incubated with 14C-leucine. The labelled material was retained by, and could be eluted from, immunoadsorbents for mouse immunoglobulins. In addition, the labelled material bound preferentially to those tumor cells for which specific blocking or ADC activities were observed. The findings indicate that factors responsible for the blocking and ADC phenomena were indeed synthesized by the spleen cells in vitro.

Antibody-dependent cell-mediated cytotoxicity for human monolayer target cells bearing blood group and transplantation antigens and for melanoma cells

A sensitive assay for antibody-dependent cell-mediated cytotoxicity (ADCMC) was developed utilizing serum from a patient with gestational choriocarcinoma and the 3H-proline microcytotoxicity test for detection fo destruction of monolayer target cells. Conditions for optimal expression of ADCMC were investigated using serum from this patient and skin fibroblasts from her husband and daugther as target cells with semi-purified blood leukocytes from normal donors as effector cells. Factors critical for optimal expression of ADCMC in this assay are the selection of effector cell donors possessing high levels of activity in the presence of serum with known lymphocyte-dependent antibody. (LDA), the effector cell preparative technique, and incubation for up to 40 h. Tris-NH4Cl lysis of red blood cells was found significantly to reduce effector cell activity. Under optimal conditions, the LDA titer of this patient's serum was greater than 10(-4). The sensitivity of the assay was confirmed by the detection of LDA activity of an anti-blood-group antibody at dilutions not demonstrating hemagglutination, and by the induction of ADCMC for blood group A antigen-bearing target cells by normal sera of B and O blood groups. In a preliminary study of sera from 16 melanoma patients on the corresponding antologous tumor target cells, four had significant LDA. Further studies are under way to determine specificty, incidence, and relationship of LDA-positive autologous sera to course of disease.