Immunogenicity of cyclophosphamide-treated leukaemia cells.

The median survival time of DBA/2Wf or CD2F1 hybrid mice increased after administration of 10(3) cells of lymphoid leukaemia L 1210 when the recipient mice were injected earlier with L 1210 cells pretreated in vivo with cyclophosphamide. To achieve this effect, at least 10(5) cells treated with cyclophosphamide should be used per mouse. This effect was immunologically specific and could not be induced by L-1 cells treated with cyclophosphamide, and was transferable by means of splenocytes. Such immunoprophylaxis was efficient for at least 100 days. Attempts at immunoprevention by means of the same cells treated with mitomycin C or killed by osmotic shock were unsuccessful.