Recombinant cysteine proteinases-based vaccines against Leishmania major in BALB/c mice: the partial protection relies on interferon gamma producing CD8(+) T lymphocyte activation

Together with poloxamer 407 as adjuvant the recombinant type I (rCPB) or type II (rCPA) cysteine proteinases of Leishmania major were screened as potential vaccines against L. major in a mouse model. The vaccines were delivered subcutaneously twice at 3 weeks intervals. Three weeks after booster injection, 5x10(5) stationary phase L. major promastigotes were inoculated subcutaneously in one footpad. Using the footpad thickness increase to monitor the clinical outcome/cutaneous lesion at site of L. major delivery, it was possible to document that rCPB but not rCPA allowed BALB/c mice to mount a partial protective response: indeed over the period under study (weeks 1-12) a clear delay was noticed after the immunization with rCPB. This partial protective effect was no more detectable if CD8 depleting antibody was given intravenously to rCPB-immunized mice, at the time of parasite challenge. Seven weeks after challenge, the draining lymph nodes were monitored for their frequencies of IFN-gamma positive CD4(+) and CD8(+) T lymphocytes using PMA and ionomycin as re-activating signals: interestingly the partial protection achieved in BALB/c mice immunized with rCPB together with poloxamer was correlated only to one immunological parameter, namely the higher frequency of IFN-gamma producing CD8(+) T lymphocytes. Of note also, in the lymph node draining the L. major-loaded footpad of C57BL/6 mice otherwise known to develop a transient lesion, the frequency of IFN-gamma producing CD8(+) T lymphocytes reach similar value 7 weeks after challenge and in absence of any prior immunization. Taken together, it was shown that the induced partial protection was mainly dependent on IFN-gamma producing CD8(+) T cells.