Induction of OVA-specific CTL response by OVA delivered with M. vaccae. C57BL/6J mice were immunized i.p. with (a) OVA alone, (b) OVA in CFA, (c) OVA plus 1 mg heat-killed M. vaccae; or with (d) OVA plus 50 µg muramyl dipeptide, (e) OVA plus 50 µg trehalose 6, 6′-dimycolate, or (f) OVA plus 1 mg heat-killed M. vaccae. Spleens were removed 10 days later and splenocytes were stimulated in vitro with E.G7-OVA cells for 6 days. The cytotoxic activities were measured using 51Cr-labelled E.G7-OVA (•), or EL4 (○). Per cent specific lysis at various effector to target ratios are shown and represent two separate experiments.