Competition for cytotoxic immune capacity against a 'syngeneic' mouse tumour distributed at two sites

Antigenic variation in cancer metastasis: immune escape versus immune control

Antigenic variation in cancer metastasis was observed in a syngeneic murine tumor system consisting of a low metastatic parental tumor line (derived from a methylcholanthrene-induced DBA/2 T lymphoma, Eb), a high metastatic spontaneous variant thereof (ESb), and a low metastatic 'revertant' from ESb (ESb-M). All three lines expressed tumor-associated transplantation antigens (TATA) which elicited specific T cell-mediated antitumor immune reactions in the host. The strongest host response was elicited upon intradermal inoculation. It could be followed by (a) the infiltration of the locally growing tumor by host cells, such as lymphocytes and macrophages, (b) the establishment of specific systemic antitumor immunity, (c) the generation of immune cells capable of transferring protective antitumor immunity into a normal syngeneic recipient, and (d) the generation of tumor specific cytotoxic T lymphocytes (CTL). Anti-TATA CTL were used as typing reagents to investigate the stability or variability in the TATA expression by cloned tumor cell lines. Antigenic variability in the TATA expression was seen under various conditions: (a) clone-dependent variation in the sensitivity to anti-TATA CTL lysis upon prolonged growth in tissue culture, (b) qualitative change in the TATA (TATA1 leads to TATA2) upon successive i.p. transplantation of the parental Eb tumor line and, (c) generation of TATA negative immune escape variants (TATA2 leads to TATA-) during metastasis formation from a s.c. site. The relative inefficiency of specific immunization procedures against ESb was found to be due to the effective generation of TATA negative variants by this highly metastatic tumor. The balance between immune control and immune escape could be influenced to the advantage of the host by some means, for instance optimizing the route of antitumor-immune sensitization or by infusion of allogeneic but H-2 identical antitumor-immune T cells. Such immune cells recognized the tumor via minor histocompatibility antigens and thus circumvented the need of TATA recognition. Finally, manipulations at the cell surface of the highly malignant ESb tumor such as those introduced in the ESb-M variant were found to dramatically effect its metastatic potential.

Analysis of synergy between cyclophosphamide therapy and immunity against a mouse tumour

C3H/He and CBA/T6T6 mice which share the H2(k) haplotype were compared for their capacity to survive challenges with the C3H-derived fibrosarcoma BP8. It was found:(1) The tumour grows at the same rate with the same median survival time in matched groups of non-immunized mice from both strains after i.p. injection of tumour cells.(2) Cyclophosphamide (Cyclo) at 10 mg/kg will cure CBA mice which have received i.p. injections of 10(7) BP8, but this dose, and more intensive treatment with this drug, fails to cure C3H mice.(3) Injecting (125)IUdR-labelled tumour cells and counting (125)I loss by whole-mouse counting shows that the cytotoxic effect of Cyclo against BP8 is similar in the 2 mouse strains.(4) Cyclo itself does not cure CBA mice, for viable tumour cells are recoverable from the peritoneal cavity 10 days after CBA mice have received 10(7) BP8 followed by 10 mg/kg Cyclo.(5) CBA mice cured of BP8 ascites by Cyclo treatment will reject further i.p. inocula of BP8.(6) The strength of immunity induced by irradiated BP8 cells was directly related to the length of exposure to this antigen. An important aspect of Cyclo treatment is that it prolongs the period during which immunity may develop.(7) Immunization of CBA mice with heavily irradiated BP8, with or without Cyclo, failed to show that Cyclo depressed the capacity of CBA mice to develop cytotoxic immunity. There was some indication that animals immunized with irradiated cells plus drug did better than those with irradiated cells alone.(8) A single injection of irradiated BP8 cells into CBA mice induced weak cytotoxic immunity, as assessed by destruction of a subsequent challenge with BP8, but these mice died from tumour more rapidly than non-immunized controls. It is suggested from these data that immunological enhancement may not always be due to blocking of cytotoxic immunity.