| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
FJ
EXPRESS SUMMARY ARTICLE The Full-length version of this article is also available, published online April 15, 2005 as doi:10.1096/fj.04-3184fje. |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
* Hebrew University Hadassah Medical School, Jerusalem, Israel; and
Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel
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
The Trimera mice model, which is based on the engraftment of human PBMC in normal strains of mice, has been successfully used to study human immune responses. On this background, we explored the possibility of using Trimera mice for establishing a novel small animal model for HIV infection that will also be useful for the study and evaluation of HIV protective vaccines and adjuvants.
PRINCIPAL FINDINGS
1. HIV-1 infection of Trimera mice
Intraperitoneal injection of T-tropic or M-tropic HIV-1 laboratory strains or clinical isolates resulted in active HIV-1 infection in the Trimera mice, but not in the control chimera mice (mice lacking human PBMC). The plasma viral load (HIV-1 RNA copies/mL) and the proviral DNA reached a peak 
14 days after i.p. injection of the virus in mice challenged with HIV-1 isolates 1 wk after the PBMC transplantation, and then gradually decreased until being undetectable 4–5 wk later (Fig. 1
A, B). Coculture of the human lymphocytes recovered from Trimera mice with HIV-1 target cells resulted in effective viral infection of the target cells (Fig. 1A, B
). With both M- tropic or T- tropic isolates, the highest viral loads (up to 106 RNA copies/mL) were achieved if the mice were challenged with the virus within the first 2 wk after the cells’ engraftment (Fig. 1C
).
|
2. Decrease of CD4+ cells and immune activation after HIV-1 infection
Within 1 wk after HIV-1 infection, a sharp decline of the engrafted human CD4 cells (80%) was observed in T- or M-tropic HIV-1-infected Trimera mice in contrast to the medium-injected Trimera animal controls. The percentage of human CD8 cells remained constant throughout the experiment in both the HIV-1-infected and noninfected Trimera mice (40±5%). Accordingly, the CD4/CD8 ratios for human lymphocytes was found to decrease only in the HIV infected Trimera mice from 1.1 (before HIV-1 injection) to 0.1 and 0.02 at 18 and 27 days after infection, respectively. Immune activation, as determined by the proportion of HLA-DR and CD38 positive cells, was also markedly enhanced in the HIV infected animals.
3. Human humoral and cellular immune responses in Trimera mice infected with HIV-1
Infection of the Trimera mice with HIV-1 resulted in the induction of human IgM and IgG anti-HIV-1 antibodies against core and envelope HIV-1 antigens. The anti-p24 and anti-gp41 IgM and IgG levels peaked 1 and 2 wk after HIV-1 inoculation, respectively.
Exposure of human lymphocytes recovered from the peritoneum of HIV-1-infected Trimera mice to HIV-1 gag-peptide, resulted in a statistically significant 2- to 3-fold increase in intracellular production of IFN-
by CD3+, CD4+, and CD8+ cells. In contrast, no increase in intracellular staining of IFN- was observed in human cells recovered from noninfected Trimera mice after exposure to HIV-1 gag-peptide (Fig. 2
).
|
CONCLUSIONS AND SIGNIFICANCE
The results of this study have demonstrated the feasibility of using Trimera mice as a murine model for HIV-1 infection (Fig. 3
) based on the following main findings: 1) Trimera mice can be readily infected with HIV-1 (both M- or T- tropic laboratory and clinical isolates) and such infection persists in the mice for over 1 month; 2) the HIV infection was found to be accompanied by extreme human T-cell activation and a rapid loss of human CD4+ T cells, thus resembling the main characteristics of HIV-1 infection in humans; and 3) the engrafted human cells can generate primary and secondary anti-HIV-1 immune responses to the ongoing HIV-1 infection.
|
Effective infection of Trimera mice was achieved with all HIV-1 isolates tested, including T-tropic or M-tropic HIV-1 laboratory strains as well as clinical isolates of different clades. The viremia generated by HIV-1 in the Trimera mice persists for at least 1 month after the infection. The decline of the viremia after a month of infection is probably a consequence of the dramatic decrease in human CD4 T cells. Though decrease of CD4 cells occurs also in noninfected Trimera mice, the much faster decline observed in the infected animals is in all probability a result of both direct killing of the CD4+ cells by the virus and extreme immune activation of the cells induced by the viral infection. This assumption is in accordance with many observations, including our finding that immune activation is better correlated with CD4 depletion in HIV-1-infected individuals than HIV-1 plasma viral load.
We have demonstrated that the human engrafted cells can elicit primary and secondary anti-HIV-1 humoral and cellular immune responses. It has already been demonstrated that the engrafted human cells, which are engrafted in significant numbers and are found in different internal organs for at least 2 months, are in a nonanergized functional status, can form mixed lymphoid follicles similar to germinal centers, and can mount primary humoral and cellular human immune responses. The capacity of the engrafted human T and B cells to be in close proximity to each other in the normal microenvironment of the mouse lymphoid tissues, is probably crucial for the generation of the human primary and secondary Ab response, manifested here by the initial production of anti-HIV-1 IgM isotype Abs followed by production of anti-HIV-1 IgG isotype Abs. Appropriate antigen presentation significantly enhances primary immune responses. The relatively weak primary response elicited in the Trimera mice by HIV-1 is therefore not surprising considering the restricted antigen presentation capabilities of the engrafted human CD14+ cells. The human T lymphocytes, recovered from Trimera mice within the first month post-transplantation, retain their proliferative capabilities and can mount primary anti-HIV-1 cellular immune responses, such as IFN- secretion after their in vitro exposure to an HIV-1 specific immunogen.
The results discussed above, together with previous studies showing the generation of primary antigen-specific human CTL response in the Trimera mice, indicate that although for a limited period of time (1 month), the Trimera mice are endowed with a viable human immune system, allowing this model to be used for evaluating potential prophylactic vaccines. In our subsequent study (Ayash-Rashkovsky et al., this issue, pages 1152–1154) we demonstrate the capacity of CpG oligonucleotides and HIV-1 antigen-pulsed dendritic cells, when coadministered to the mice, to confer them protection from subsequent HIV-1 infection. This novel small animal model for HIV-1 infection offers an attractive tool for testing potential antivirals, studying the interaction of host immune system and HIV-1, and most importantly, it may serve as a platform for screening and developing potential HIV-1 protective vaccines and adjuvants.
FOOTNOTES
To read the full text of this article, go to http://www.fasebj.org/cgi/doi/10.1096/fj.04-3184fje; doi: 10.1096/fj.04-3184fje
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
