Tumor immunity to murine plasma-cell tumors. VIII. Immunosuppression of the generation of cytotoxic T cells by murine plasma-cell tumor lines

Cure of mice bearing a late-stage, highly metastatic, drug-resistant tumor by adoptive chemoimmunotherapy

We show here that in contrast to BALB/c mice bearing a late-stage, large MOPC-315 plasmacytoma, BALB/c mice bearing a late-stage, large RPC-5 plasmacytoma were not cured by cyclophosphamide therapy (15, 50, 100 or 200 mg/kg). However, most BALB/c mice bearing a late-stage RPC-5 tumor were cured by cyclophosphamide therapy (100 mg/kg) in conjunction with adoptive immunotherapy using tumor-infiltrated spleen cells (TISpC) that had been cultured with inactivated RPC-5 tumor cells plus polyethylene glycol 6000, even though this protocol was not effective for the therapy of mice bearing a barely palpable, early-stage RPC-5 tumor. Only a few of the mice that were cured of a late-stage RPC-5 tumor following adoptive chemoimmunotherapy (ACIT) were resistant to a subsequent challenge with RPC-5 tumor cells. However, the challenged mice that had developed progressively growing tumors could then be cured by cyclophosphamide alone when the tumor became large, even though this treatment was not curative for mice bearing a tumor of similar size but not previously treated by ACIT. Thus, the cure by ACIT of BALB/c mice bearing a lethal, late-stage RPC-5 tumor with extensive metastases provides a novel experimental tumor model for investigating the mechanisms by which a chemotherapeutic drug and adoptive cellular immunotherapy can cooperate in causing the complete regression of a large tumor load.

Defective T helper activity in the spleen of BALB/c mice immune to a syngeneic fibrosarcoma

BALB/c mice were immunized with the syngeneic 3-methylcholanthrene-induced fibrosarcoma CA-2 by the growth and excision method. When lymphoid cells from different organs of these tumor-free mice were tested in a direct 51Cr-release assay, peritoneal exudate cells but not spleen cells displayed specific cytotoxicity against the syngeneic tumor target. A cytotoxic response could be obtained by tumor-immune spleen cells when cultured in a mixed lymphocyte tumor cell culture (MLTC) at high but not low density although at the same effector/stimulator ratio. Lack of cytotoxic activity in low density MLTC was not due to an impairment of cytotoxic precursors since cytotoxicity was rescued by adding exogenous interleukin-2 in experimental conditions in which no lymphokine-activated killer cells could develop relevant anti-CA-2 lysis. When low density MLTC were supplemented with either 800 R-irradiated cells or nonirradiated, negatively selected Lyt 1+ cells from the same immune mice, induction of a cytotoxic response against CA-2 occurred and interleukin-2 production became detectable. Additional studies indicated that spleen cells of CA-2-immune mice were also impaired in their ability to provide help to syngeneic thymocytes for the generation of cytotoxic T lymphocytes against C57BL/6J alloantigens. Dilution effect of helper cells due to immunization procedures was excluded since spleen cells of mice immunized against another BALB/c tumor, the YC8 lymphoma, or against DBA/2 minor histocompatibility antigens provided good help to thymocytes against the same alloantigens. These results indicate that tumor-immune animals may also have selective T helper defects in an important lymphoid organ like spleen.

Paired Epstein-Barr virus-carrying lymphoma and lymphoblastoid cell lines from Burkitt's lymphoma patients: comparative sensitivity to non-specific and to allo-specific cytotoxic responses in vitro

Paired Epstein-Barr (EB) virus-carrying cell lines have been established from Burkitt's lymphoma (BL) patients; one the BL-cell line derived from the malignant cells of the tumour and bearing the relevant chromosomal translocation, the other the diploid lymphoblastoid cell line (LCL) derived from the patient's normal B cells by experimental infection with the virus. Comparative studies have shown that both BL and LCL cells are relatively resistant to fresh NK cells but are more susceptible to in vitro-activated NK cells; individual pairs differ as to whether the BL or LCL cells are more sensitive to such effectors. With most cell pairs studied, the two cell types were equally efficient at inducing NK-cell activation in vitro. When the in vitro stimulation protocol was changed to favour the induction of allo-specific responses, most BL cells were noticeably poorer stimulators than the corresponding LCL although both cell types induced a similar pattern of cytotoxicity; this appeared to be directed against HLA class I allo-antigens and could be inhibited by class I antigen-specific monoclonal antibodies. Most BL target lines, though susceptible to this allo-specific lysis, were significantly less so than the corresponding LCL However, only 1/7 BL-cell lines tested vis-à-vis the LCL gave evidence of a gross reduction in HLA antigen expression and this was immediately apparent from both serological typing and cellular analysis.