Modification of the antitumor action of Corynebacterium parvum by stress

Social grouping and isolation of mice, in the presence of an acute stressor, were found to differentially affect the antitumor action of the immunological adjuvant Corynebacterium parvum. Socially grouped DBA/2j mice were injected intradermally with P815 mastocytoma ascites cells. Half the mice had a threshold dose of C. parvum admixed with the P815 cells. Half the mice in each of those conditions were given acute, inescapable electric footshock. In a second experiment, the stressed mice were socially isolated prior to the acute stress. Tumor growth itself was not affected by the stress procedures. C. parvum inhibited tumor growth in non-stressed and socially isolated, stressed mice. However, social grouping selectively negated the C. parvum effect resulting in tumor growth and mortality equivalent to mice not given the adjuvant. Psychological factors may be important to the development of concomitant immunity and the efficacy of immunotherapies.