Immune rejection of intracerebral gliomas using lymphocytes from glioma-bearing rats.

Naturally occurring malignancies do not induce immune responses against cancer antigens. Is the lack of an immune response caused by an antigen presentation defect or by induced antigen-specific immune suppression? The current study was performed to determine whether a progressing intracerebral malignancy affects production of peripheral autologous glioma antigen-specific immune responses. Peripheral immunization of both glioma-bearing and non-glioma-bearing animals with cancer cells and adjuvant generated similar levels of glioma antigen-specific cytotoxic T lymphocyte activity. However, immune cell populations from glioma bearers were significantly less efficient than immune cell populations from non-cancer bearers in their ability to reject progressing intracerebral tumors. A variety of manipulations designed to reduce nonspecific immune suppression in vivo and in vitro had no effect on the in vivo efficacy of the activated T-lymphocyte populations. The presence of progressing tumors appeared to augment rather than suppress cancer antigen-specific responses, leading to the speculation that reduced efficacy was caused not by generalized immune suppression but rather by a reduction in the number of immune effector cells by either clonal anergy or clonal deletion. Most importantly, the data demonstrated that, despite decreased in vivo efficacy, immune effector cells capable of rejecting an intracerebral malignancy could be generated from cancerous hosts.