Cytokine Production Patterns And Lymphoproliferative Responses In Volunteers Orally Immunized With Attenuated Vaccine Strains Of Salmonella Typhi

Abstract

New recombinant strains of attenuated Salmonella typhi used as live oral vaccines elicit potent immune responses. This study examined the patterns of cytokine production and proliferation to specific S. typhi antigens in subjects orally immunized with attenuated S. typhi vaccines CVD 906, CVD 908, and CVD 908 expressing the circumsporozoite protein of Plasmodium falciparum. After immunization, sensitized lymphocytes were found in subjects' blood that exhibited significantly increased proliferative responses and interferon-gamma production to purified S. typhi flagella when compared with preimmunization levels. Significant negative correlations were observed between interleukin-4 production and both interferon-gamma production and proliferation to S. typhi flagella. These results demonstrate that oral immunization with attenuated S. typhi strains alone or with those carrying a foreign gene elicits strong systemic cell-mediated immunity to purified S. typhi antigens, including the production of cytokines compatible with T1-type responses.

Cell-mediated immune responses in humans after immunization with one or two doses of oral live attenuated typhoid vaccine CVD 909

“…Except for 2 of the 8 subjects in the Ty35000 study who showed meager, and probably biologically inconsequential, increases in IL-5 production in response to TypVac in post-immunization samples (i.e., in Vol#35000-5 day 28 post-vaccination levels were 5.7 pg/ml compared to a pre-vaccination level of 2.5 pg/ml, while Vol# 35000-2 showed 12.9 pg/ml at day 60 postvaccination compared to a pre-vaccination level of 3.2 pg/ml), there were no other significant increases in IL-5, IL-4 and IL-2 production after immunization with CVD 909 (Table 1). These results are consistent with previous findings using other attenuated S. Typhi strains [8,19,20,23,26] that also showed a dominance of Th1 responses (e.g., IFN-γ and TNF-α production), suggesting that these cytokines are likely to be important in S. Typhi immunity. Similar to the results with proliferative responses, no differences were observed between volunteers immunized with one or two doses of CVD 909.…”

“…Over the past decade we showed that immunization with several strains, including Ty21a (the licensed vaccine), CVD 906 (an ΔaroC ΔaroD mutant), CVD 908 (an ΔaroC ΔaroD mutant) and CVD 908htrA (an ΔaroC ΔaroD ΔhtrA mutant) resulted in the appearance in peripheral blood of sensitized lymphocytes that exhibit significantly increased proliferative responses and cytokine production, as well as classical and non-classical classI restricted CTL activity to purified S. Typhi antigens and S. Typhi-infected targets [5][6][7][17][18][19][20]23,25]. Moreover, we have shown that a single dose of CVD 909 also induced lymphoproliferative responses [21].…”

“…In the latter study, from a total of 8 volunteers who were immunized, PBMC were not available from volunteer 35000-5 at day 60 and from volunteer 35000-8 at day 28. PBMC were isolated immediately after the blood draws by density gradient centrifugation and cryopreserved in liquid N 2 following standard techniques until used in the assays [20,23].…”

“…Typhi flagella H-antigen-Flagellar antigen was purified from the rough S. Typhi strain Ty2R following standard procedures and used at a concentration of 2 or 10 μg/ml as indicated in the text [8,23].…”

“…The bacterial pellet was resuspended to a concentration of 1X10 7 organism/ml in serum free media and kept at 4°C until used [23].…”