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FJ
EXPRESS SUMMARY ARTICLE The Full-length version of this article is also available, published online April 15, 2005 as doi:10.1096/fj.04-3185fje. |
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* Hebrew University Hadassah Medical School, Jerusalem, Israel;
Coley Pharmaceutical Group, Ottawa, Ontario, Canada; and
Immune Response Corporation, San Diego, California, USA
1 Correspondence: G. B., Animal Sciences, Faculty of Agriculture, Hebrew University, Rehovot 76701, Israel. E-mail: borkow{at}agri.huji.ac.il; Z. B., Rosetta Genomics, 10 Plaut St., Science Park, Rehovot 76701, Israel. E-mail: zbentwich{at}rosettagenomics.com
SPECIFIC AIMS
We have recently developed a novel mouse animal model for HIV-1 infection (Ayash-Rashkovsky et al., this issue, pages 1149–1151). In the present study, our main aim was to demonstrate the capacity of this model to serve as a platform for rapid testing of candidate HIV-1 vaccines and adjuvants.
PRINCIPAL FINDINGS
1. Induction of human primary immune responses in Trimera mice immunized with HIV-1 immunogen
Trimera mice, injected and boosted with autologous monocyte-derived DCs, previously pulsed in vitro with an HIV-1 immunogen, generated significantly higher levels of human IgM and IgG against p24 than control mice injected with nonpulsed DCs. There was a 5- to 8-fold increase in the percent of human lymphocytes recovered from the immunized Trimera mice that produced IFN-
after exposure to the HIV-1 immunogen, but not in human lymphocytes recovered from Trimera mice injected with nonpulsed DCs (Fig. 1
, compare upper panels with middle panels).
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2. Enhancement of HIV-1 specific immune response with immunostimulatory CpG ODN
ODNs containing CpG motifs enhance humoral and cellular specific immunity via interaction with the highly conserved microbial pattern recognition receptor TLR-9. The vast majority (>84%) of plasmacytoid dendritic cells (pDC), monocytes, and B cells, recovered from the mice peritoneum 7 or 14 days after PBMC transplantation, expressed TLR-9. Based on the high expression of TLR-9 in these cells after transplantation, we tested the effect of class B CpG ODN on our immunization experiments. Addition of the CpG ODN to the immunization protocols resulted in significantly higher levels of IgM and IgG anti-p24 Abs. Only sera obtained from mice immunized with HIV-1 immunogen-pulsed DCs and CpG ODN, exhibited neutralizing activity. A marked enhancement (up to 30-fold) of the cellular anti-HIV-1 immune responses was observed after the addition of class B CpG ODN to the immunization protocol (Fig. 1
, lower panel).
3. Protection of immunized Trimera mice from HIV-1 infection
Mice immunized with DCs pulsed with the HIV-1 immunogen and class A CpG ODN (Fig. 2
) were protected from challenge with either HIV-1 of clade A or E. All animals had undetectable plasma viral load and no syncytia formation occurred in coculture experiments with human lymphocytes obtained from all mice in the group (Fig. 2)
. In contrast, mice injected with DCs only, were not protected against either challenge with HIV-1 clade A or E. Similar results were obtained with class B CpG ODN (Fig. 2)
.
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CONCLUSIONS AND SIGNIFICANCE
This study demonstrates that the Trimera-HIV-1 model can be used as a platform for testing new approaches for enhancing anti-HIV specific immunity and for rapid examination of potential HIV-1 protective vaccines, based on the following main findings: 1) the engrafted human cells generated primary and secondary anti-HIV-1 immune responses after immunization with an HIV-1 immunogen presented on autologous DC; 2) CpG ODN enhanced both humoral and cellular HIV-1 specific immune responses; and 3) the mice were protected from HIV-1 infection after their immunization with the combination of gp120-depleted HIV-1 antigen-loaded autologous human DCs and CpG ODN.
We have demonstrated that the human-engrafted cells can elicit primary and secondary anti-HIV-1 humoral and cellular immune responses, not only to ongoing HIV-1 infection (Ayash-Rashkovsky et al., this issue), but also after immunization. The engrafted human cells, which are found in different internal organs for at least 2 months in a nonanergized functional status, can form mixed lymphoid follicles similar to germinal centers and mount primary humoral and cellular human immune responses. The human T lymphocytes, recovered from Trimera mice, retain their proliferative capabilities and can mount primary anti-HIV-1 cellular immune responses, manifested by the intracellular IFN- secretion after their in vitro exposure to an HIV-1 immunogen. This and previous studies demonstrating the generation of primary antigen-specific human CTL response in Trimera mice, indicate that the Trimera mice are endowed with a viable human immune system, capable of protecting the mice from subsequent challenge by HIV-1.
The high levels of TLR-9, the receptor of CpG ODN, found in different antigen presenting cell subsets, both in the transplanted PBMC and in the recovered human cells from the mice peritoneum, encouraged us to explore the use of CpG ODN for immunization and boosting in our model. This approach has been previously shown to enhance the efficacy of immunization in a murine colon carcinoma model, in which large established tumors that resist chemotherapy were eliminated. We found that immunization of the Trimera mice with autologous DCs pulsed with gp120-depleted HIV-1 antigen coadministered with class B CpG ODN significantly enhanced both the anti-HIV-1 humoral and cellular immune responses in the Trimera mice. Remarkably, Trimera mice immunized with HIV-1 immunogen-pulsed DCs coinjected with class A CpG ODN 2216 were protected from subsequent HIV-1 infection in two separate experiments, as determined by testing HIV-1 viral load, proviral DNA, and active virus replication. Complete protection was also achieved when the mice were immunized with HIV-1 immunogen-pulsed DCs coinjected with class B CpG ODN 2397 and challenged with HIV-1 clade A. However, with class B CpG ODN 2397, in a second experiment, when the mice were challenged with HIV-1 clade E, the protection was only partial. As expected, DCs in the Trimera model acted as nature’s adjuvant, allowing the generation of immune resistance to HIV-1. We suggest that antigen-loaded DCs prime the engrafted human lymphocytes, eliciting the formation of antigen-specific IFN--producing Th1 type CD4+ helper cells, which induce antigen specific B cells to proliferate and produce anti-HIV-1 Abs. These Th1 helper cells are probably critical in activating antigen-specific anti-HIV-1 CD8+ T lymphocytes. Altogether, these immune responses resulted in resistance to the subsequent HIV-1 challenge.
The levels of specific anti-p24 antibody, both of IgM and IgG isotypes, and the percentage of HIV-1 antigen specific IFN--secreting human T cells, were significantly higher in Trimera mice immunized with HIV-1 immunogen-pulsed DCs with class B CpG ODN, than those immunized without CpG ODN or injected with DCs only. On the whole, the potential of generating specific anti-HIV-1 Abs in this model is established. In spite of the significant humoral responses generated in the immunized Trimera mice in two experiments, the elicited Abs exhibited only very low neutralizing activity against the native virus in vitro.
The Trimera mice model can also be used for the purpose of studying the effectiveness of potential vaccines and adjuvant in hosts with preexisting biased immune profiles.
Our two studies (Ayash-Rashkovsky et al., this issue, pages 1149–1151) demonstrate that the new murine model for HIV infection in Trimera mice may be used to test the efficacy of candidate HIV-1 protective vaccines and of immunomodulating adjuvants such as CpG ODNs. The Trimera-HIV-1 model offers an attractive tool for testing potential HIV vaccines as well as for studying several aspects of the interaction between the host immune system and HIV. The wide scope and utility of this model require further exploration and pose an exciting challenge to both immunologists and virologists, especially in view of the growing difficulties with primate experimentations.
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FOOTNOTES
To read the full text of this article, go to http://www.fasebj.org/cgi/doi/10.1096/fj.04-3185fje; doi: 10.1096/fj.04-3185fje
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