CD4+ T cell-independent DNA vaccination against opportunistic infections

Abstract

Depletion or dysfunction of CD4 + T lymphocytes profoundly perturbs host defenses and impairs immunogenicity of vaccines. Here, we show that plasmid DNA vaccination with a cassette encoding antigen (OVA) and a second cassette encoding full-length CD40 ligand (CD40L), a molecule expressed on activated CD4 + T lymphocytes and critical for T cell helper function, can elicit significant titers of antigen-specific immunoglobulins in serum and Tc1 CD8 + T cell responses in CD4-deficient mice. To investigate whether this approach leads to CD4 + T cell-independent vaccine protection against a prototypic AIDS-defining infection, Pneumocystis (PC) pneumonia, we used serum from mice vaccinated with PC-pulsed, CD40L-modifed DCs to immunoprecipitate PC antigens. Kexin, a PC antigen identified by this approach, was used in a similar DNA vaccine strategy with or without CD40L. CD4-deficient mice receiving DNA vaccines encoding Kexin and CD40L showed significantly higher anti-PC IgG titers as well as opsonic killing of PC compared with those vaccinated with Kexin alone. Moreover, CD4-depleted, Kexin-vaccinated mice showed a 3-log greater protection in a PC challenge model. Adoptive transfer of CD19 + cells or IgG to SCID mice conferred protection against PC challenge, indicating a role of humoral immunity in the protection. The results of these studies show promise for CD4-independent vaccination against HIV-related or other opportunistic pathogens.

Immunization with Pneumocystis Cross-Reactive Antigen 1 (Pca1) Protects Mice against Pneumocystis Pneumonia and Generates Antibody to Pneumocystis jirovecii

“…A number of potential vaccine candidates have been evaluated in animal models of PcP as well, but at best, they achieved only partial protection (15,(23)(24)(25)(26)(27). A recent publication also describes boosting naturally acquired antibody in Pneumocystisexposed animals with a fragment of kexin as a means to enhance immune response to Pneumocystis (28).…”

“…The vaccination strategy could also be optimized to function in a T cell-independent fashion through adjuvants of conjugation. Additionally, it could be used in CD4 ϩ T cellindependent platforms such as DNA vaccination (27).…”

Overcoming Hurdles to Development of a Vaccine against Pneumocystis jirovecii

“…Several groups have examined the use of the Pneumocystis protease kexin (KEX1) as a potential vaccine target (18). Zheng et al (2005) used DNA expressing the P. murina kexin and CD40 ligand (CD40L) in CD4 T cell-depleted mice to demonstrate that kexin-specific antibodies were produced corresponding to about a 100-fold reduction in P. murina lung burden (19). Interestingly, the antibodies recognized a 55-kDa protein on Western blots that was likely the same protein recognized by immunization with protein preparations from whole organisms (16,17,19).…”

“…Zheng et al (2005) used DNA expressing the P. murina kexin and CD40 ligand (CD40L) in CD4 T cell-depleted mice to demonstrate that kexin-specific antibodies were produced corresponding to about a 100-fold reduction in P. murina lung burden (19). Interestingly, the antibodies recognized a 55-kDa protein on Western blots that was likely the same protein recognized by immunization with protein preparations from whole organisms (16,17,19). This group also demonstrated that antibodies raised to kexin in mice cross-reacted with Pneumocystis isolated from nonhuman primates (19).…”

“…Interestingly, the antibodies recognized a 55-kDa protein on Western blots that was likely the same protein recognized by immunization with protein preparations from whole organisms (16,17,19). This group also demonstrated that antibodies raised to kexin in mice cross-reacted with Pneumocystis isolated from nonhuman primates (19). This past year, Kling and Norris demonstrated that immunization of nonhuman primates with KEX1 resulted in high titers of specific antibody and protection against PCP for almost 36 weeks after immunosuppression using infection with simian immunodeficiency virus (SIV) or HIV and exposure to Pneumocystis (20).…”