Expression of CD40L by the ALVAC-simian immunodeficiency virus vector abrogates T cell responses in macaques

Isabela Silva de Castro, Shari N. Gordon, Jun Liu, Massimiliano Bissa, Katherine McKinnon, Hung V. Trinh, Melvin N. Doster, Luca Schifanella, Namal P. Liyanage, Jin Chao Cao, Olivia Cheng, Kathryn Foulds, Mario Roederer, Richard A. Koup, Xiaoying Shen, Georgia D. Tomaras, David J. Venzon, Donald N. Forthal, Timothy Fouts, David C. MontefioriJim Tartaglia, Mangala Rao, Mario Ostrowski, Genoveffa Franchini, Monica Vaccari

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6 Scopus citations


Immunization with recombinant ALVAC/gp120 alum vaccine provided modest protection from human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) acquisition in humans and macaques. Vaccine-mediated protection was associated with the elicitation of IgG against the envelope V2 loop and of envelope-specific CD4+ T cell responses. We hypothesized that the simultaneous expression of the costimulatory molecule CD40L (CD154) by the ALVAC-HIV vector could increase both protective humoral and cellular responses. We engineered an ALVAC-SIV coexpressing CD40L with SIVmac251 (ALVAC-SIV/CD40L) gag, pol, and env genes. We compared its immunogenicity in macaques with that of a canonical ALVAC-SIV, with both given as a vector-prime/gp120 in alum boost strategy. The ALVAC-SIV/CD40L was superior to the ALVAC-SIV regimen in inducing binding and tier 1 neutralizing antibodies against the gp120. The increase in humoral responses was associated with the expression of the membrane-bound form of the CD40L by CD4+ T cells in lymph nodes. Unexpectedly, the ALVAC-SIV/CD40L vector had a blunting effect on CD4+ Th1 helper responses and instead favored the induction of myeloid-derived suppressor cells, the immune-suppressive interleukin-10 (IL-10) cytokine, and the down-modulatory tryptophan catabolism. Ultimately, this strategy failed to protect macaques from SIV acquisition. Taken together, these results underlie the importance of balanced vaccine-induced activating versus suppressive immune responses in affording protection from HIV. IMPORTANCE CD40-CD40 ligand (CD40L) interaction is crucial for inducing effective cytotoxic and humoral responses against pathogens. Because of its immunomodulatory function, CD40L has been used to enhance immune responses to vaccines, including candidate vaccines for HIV. The only successful vaccine ever tested in humans utilized a strategy combining canarypox virus-based vector (ALVAC) together with an envelope protein (gp120) adjuvanted in alum. This strategy showed limited efficacy in preventing HIV-1/SIV acquisition in humans and macaques. In both species, protection was associated with vaccine-induced antibodies against the HIV envelope and CD4+ T cell responses, including type 1 antiviral responses. In this study, we tested whether augmenting CD40L expression by coexpressing it with the ALVAC vector could increase the protective immune responses. Although coexpression of CD40L did increase humoral responses, it blunted type 1 CD4+ T cell responses against the SIV envelope protein and failed to protect macaques from viral infection.

Original languageEnglish (US)
Article numbere01933-19
JournalJournal of virology
Issue number6
StatePublished - Feb 2020

Bibliographical note

Funding Information:
This work was supported by the intramural U.S. National Cancer Institute (NCI) program. We acknowledge the following institutions for the grants supporting the authors: M. Ostrowski was supported by Canadian Institutes of Health Research (CIHR) grant THA-11906. Salary support for M. Ostrowski was provided by Ontario HIV Treatment Network (OHTN) grant AHRC G769. Contributions were made by the extramural NIAID program (grant HHSN27201100016C to X. Shen, G. D. Tomaras, and D. C. Montefiori), the Henry M. Jackson Foundation (HJF), the U.S. Department of Defense, and Collaboration for Aids Vaccine Discovery (CAVD) grants OPP1032325 (R. A. Koup) and OPP1147555 (R. A. Koup) from the Bill and Melinda Gates Foundation. H. V. Trinh and M. Rao were supported by a cooperative agreement (W81XWH-18-2-0040) between the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc., and the U.S. Department of Defense. H. V. Trinh was partially supported by a grant from the Swiss National Science Foundation (P3SMP3_148406/1).

Publisher Copyright:
© 2020 American Society for Microbiology. All rights reserved.


  • CD4
  • CD40L
  • HIV
  • MDSC
  • Macaques
  • NHP
  • SIV
  • Vaccine


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