Increased susceptibility to inoculated Lewis lung carcinoma (3LL) but unaltered tumor growth in mice treated with monoclonal antibody to L3T4 on mouse T-helper cells.

The importance of different lymphocyte cell populations in early recognition and destruction of tumor cells has not been fully established. Certainly natural killer cells and cytotoxic T lymphocytes are involved. Using a recently developed monoclonal antibody (GK 1.5) that has been shown to have in vivo cytotoxic activity directed at L3T4-bearing T cells, we provide in these experiments evidence that T-helper cells are also important in early antitumor immunity. Development of progressive tumor growth after the subcutaneous inoculation of 10(5) Lewis lung carcinoma (3LL) cells was greater in antibody-treated mice (13 of 20 treated mice vs. 6 of 21 controls). Nevertheless, in those animals that developed tumors, the latentcy period (time from tumor cell inoculation until tumor first palpable) and tumor growth rate were no different in antibody-treated mice when compared with control animals. In subsequent experiments, animals were exposed to irradiated tumor cells in Freund's adjuvant on three occasions and tumor growth was then assessed. Growth was slower in the sensitized group. Administration of GK 1.5, however, did not enhance the tumor growth rates in either the previously sensitized or control groups. The results suggest that T-helper cells might be of greater functional importance in early tumor cell recognition and destruction and of lesser importance in the restraint of tumor growth, once the tumor has become established.