An Alternative and Effective HIV Vaccination Approach Based on Inhibition of Antigen Presentation Attenuators in Dendritic Cells

Background Current efforts to develop HIV vaccines that seek to stimulate immune responses have been disappointing, underscoring the inability of natural immune responses to control HIV-1 infection. Here we tested an alternative strategy to induce anti-HIV immune responses by inhibiting a host's natural immune inhibitor. Methods and Findings We used small interfering RNA (siRNA) to inhibit suppressor of cytokine signaling (SOCS) 1, a key negative regulator of the JAK/STAT pathway, and investigated the effect of this silencing on the ability of dendritic cells (DCs) to induce anti-HIV-1 immunity. We found that SOCS1-silenced DCs broadly induced enhanced HIV-1 envelope (Env)-specific CD8+ cytotoxic T lymphocytes and CD4+ T helper cells, as well as antibody responses, in mice. Importantly, SOCS1-silenced DCs were more resistant to HIV Env-mediated suppression and were capable of inducing memory HIV Env-specific antibody and T cell responses. SOCS1-restricted signaling, as well as production of proinflammatory cytokines such as interleukin-12 by DCs, play a critical role in regulating the anti-HIV immune response. Furthermore, the potency of HIV DNA vaccination is significantly enhanced by coimmunization with SOCS1 siRNA expressor DNA. Conclusions This study demonstrates that SOCS1 functions as an antigen presentation attenuator to control both HIV-1-specific humoral and cellular responses. This study represents the first, to our knowledge, attempt to elicit HIV-specific T cell and antibody responses by inhibiting a host's antigen presentation attenuator, which may open a new and alternative avenue to develop effective therapeutic and prophylactic HIV vaccines.

Sub-cutaneous (S/C) interleukin (IL)-2, administered with ART, increases CD4 T-cell numbers [18][19][20][21] and recall antigen-specific CD4 lymphocyte proliferation [22,23]. However timing may be crucially important to the induction of cell-mediated responses [24]. We have previously shown that IL-2 administration subsequent to immunization was associated with boosted responses to the antigen in question, suggesting a therapeutic role for IL-2 in enhancing proliferative T-cell responses in HIV-1 infection [2,25].
We investigated the ability of Remune™ and IL-2, combined and separately, to induce HIV-1-specific CD4 and CD8 T-cell responses in chronically HIV-1-infected patients on ART in an observational, open-label, randomized, pilot study. We also assessed antigen-specific IL-4 release as this cytokine plays a role in balance and/or suppression of cell-mediated responses [26,27], We report here evaluation of specific T-cell proliferation, antigenspecific IL-4 release, CD8 T-cell IFN-γ responses and neutralizing antibody titres, in order to comprehensively describe the specific immune response relevant to control of viral replication.

Patients and Study Design
In this observational, phase I, pilot study conducted at Chelsea and Westminster Hospital, London, 36 antiretroviral-naive patients were initiated on ART at week 0, which was continued for the duration of the study. ART comprised 2 nucleoside analogues and one protease inhibitor or non-nucleoside reverse transcriptase inhibitor. At week 17 patients were randomized to receive immunotherapy with IL-2 and/or therapeutic immunisation with a gp120depleted whole inactivated HIV-1 immunogen. Sufficient Remune™ was donated for use in 20 patients by Immune Response Corporation (IRC), Carlsbad, CA, USA. Patients were randomized at week 17 only if their viral load was <50 copies ml/plasma and CD4 T-cell count was ≥ 300 cells/μl blood at week 16. Treatment groups for randomization were as follows: A) ART alone (n = 9); B) ART plus IL-2 (Proleukin™) (n = 11); C) ART plus IL-2 and Remune™ (n = 7); and D) ART plus Remune™ (n = 9). IL-2 (5 × 10 6 U) was administered S/C, twice daily, for 5 days at weeks 17, 21 and 25. 100 μg Remune™ was administered I/M at weeks 17, 29, 41 and 53. Laboratory analysis was conducted at weeks--6, -3 and 0 before ART, and weeks 1,2,4,8,16,17,21,25,29,41, 53 and at study completion at week 65. The primary outcome was induction of positive changes in lymphocyte proliferative responses to HIV-1 antigens. In addition to the main study time points, a further sub-study of viral loads and lymphocyte subset numbers was conducted in a sub-set of patients (n = 15) receiving IL-2 in groups B and C on the 5 th day of each IL-2 cycle, i.e. at weeks 18, 22 and 26. This sub-study was initiated after the main study had begun and included all patients receiving IL-2 in groups B and C from the date of its inception. Appropriate regulatory approval was granted by Riverside Ethics Committee and patients gave written informed consent.

Lymphocyte Proliferative Assays
Proliferation assays and supernatant collection for IL-4 assessment were conducted as previously described [2]. Stimulation indices (SI) for triplicates (standard error <15%) were calculated as antigen-stimulated β-particle counts per minute (cpm)/no antigen cpm. A positive response was regarded as a SI >5.

Measurement of Cytokine Production
IL-4 bioassays were carried out as previously described [2] using IL-4 (CT.h4S) dependent cell lines. Briefly, IL-4 was measured in culture supernatants of HIV-1 antigen stimulated proliferation assays. Proliferation of the IL-4dependent cell line CT.h4S was measured by incorporation of tritiated thymidine. Results are presented as IL-4 driven cpm.

Delayed hypersensitivity (DTH) tests to Remune™
In vivo delayed-type hypersensitivity (DTH) skin tests to Remune™ antigen were performed to assess HIV-1-specific cell-mediated immune responses as described elsewhere [29] in all patients at weeks 17, 29 and 53.

Statistical Analysis
Changes in lymphocyte subsets and viral load between week 0 and 16, weeks 0 and 65 and weeks 16 and 65, were assessed using the Wilcoxon Signed Rank test. Prolifera-tion and IL-4 data were assessed with repeated measures analysis of variance using MIXED procedure in SAS statistical software. For log-transformed antigen-specific proliferative stimulation indices, between and within subject weeks 0 to 17, weeks 17 to 65 and weeks 0 to 65, adjusted separate slopes were estimated for each study arm with 95% confidence interval. Differences in overall viral load from week 18-26, between groups B and C were assessed using the Pearson Chi-squared test.

Patient demographics
Fifty two anti-retroviral naïve patients were screened for this study which was carried out at the Chelsea and Westminster Hospital, London over a six year period. Of the screened patients 16 dropped out prior to randomisation at week 17. All the remaining 36 patients who were randomised completed the study. The mean age of patients at study entry was 38.75 years. There was one female patient (2.78%) and 100% of patients were of white European ethnicity.

Viral loads and CD4 T-cell counts
Median viral loads and CD4 T-cell counts for each group are depicted in Figure 1. The median week 0 viral load for all patients was 88,699 copies/ml plasma (range 50-779,254). The median absolute CD4 T-cell count was 294 cells/μl whole blood (range 76-551). Nineteen of 36 patients (53%) had CD4 T-cell counts below 300 cells/μl blood at pre-ART time points.
By week 17 the median viral load in all groups was less than 50 copies. All patients, except 5 (one in Group A, three in Group B, one in group D), maintained viral suppression at the main study time points from week 17 onwards while receiving ongoing ART. One patient in Group C (patient 11) elected to discontinue ART at week 47 causing subsequent rebound in viraemia. At week 17 the median CD4 T-cell count in each complete group was as follows: Group A, 456 cells/μl (range 261-673) ( Figure  1A); Group B, 377 cells/μl (range 81-742) ( Figure 1B); Group C, 468 cells/μl (range 306-680) ( Figure 1C); Group D, 337 cells/μl (range 289-702) ( Figure 1D). IL-2induced increases in absolute CD4 T-cell counts are also apparent in groups B and C. By week 65 these values were 602 cells/μl (range 300-918) for Group A, 731 cells/μl (range 253-1025) for Group B, 619 cells/μl (range 358-1404) for Group C and 505 cells/μl (range 345-768) for Group D.

Lymphocyte proliferation to HIV-1 antigens
HIV-1-specific proliferative responses increased transiently for many patients. Regression analysis of these responses revealed no significant changes in group A ( Fig.  2A). In group-B from week 0 to 65 a significant increase in the np24 response (p = 0.005) was observed (Fig. 2B). In group C no increase in HIV-1-specific proliferative responses were seen (Fig. 2C). Of note was an outstanding response to Remune™ with an SI of 95 at week 65 for patient 11 in this group (data not shown) coincident with rebound viraemia (152,536 copies/ml) following selfimposed ART discontinuation. In group D a positive regression was seen in responses to Nef (p = 0.004) and whole Remune™ antigen (p = 0.005) from week 0 to 65. (Fig. 2D). The only response which significantly increased between week 17 and 65 in any group was the p24 response in group D (p = 0.039). Patient 8 in this group demonstrated a very large response to Remune™ (SI = 261) and np24 (SI = 144) at week 29 following breakthrough of resistant virus at week 25 (6,315 copies/ml) (data not shown). No other substantial increases in responses occurred between week 17 and 65 for any group or at any time point between the groups.

In vivo delayed type hypersensitivity reactions to Remune™
Induration size of hypersensitivity reactions to Remune™ did not become positive (>9 mm diameter) in any patient at any of the time points tested (weeks 17, 29 and 53).

Lymphocyte proliferation to recall antigens
Baseline to week 16 T-cell responses have been described in detail previously [1]. Regression analysis revealed significant increases in recall responses in all groups between week 0 and 65 ( In group A PPD and tetanus responses showed significant positive regressions over the 65 weeks (p = 0.018 and p = 0.018 respectively); in group B only the PPD response regression curve was significant (p = 0.044); and in group C only the tetanus response was significant (p = 0.0003). There were no significant differences in recall responses between treatment groups.

HIV-1-specific IL-4 production
Antigen-specific IL-4 production may be associated with suppression of proliferative responses and dampening of inflammatory immune responses. Therefore we measured IL-4 production in proliferation assay culture supernatants in response stimulation with each HIV-1 antigen, as previously described [1]. Significant increases in HIV-1specific IL-4 production from weeks 17 to 65 were observed in response to p24 in group-B (p = 0.023), and group C (p = 0.032) and in response to gp120 in group D (p = 0.037) (Fig. 3A). HIV-1-specific IL-4 production did not significantly increase in group A (data not shown).
We observed an apparent relationship between IL-4 production and loss/lack of proliferation in 17 of 28 patients tested, distributed evenly between groups, evident from week 0 to 16 and week 17 to 65. Patient 11 (group C) is shown as an example, where HIV-1-specific proliferative responses to p24, gp120, nef and Remune™ are high at week 29 ( Fig. 3B) with absence of IL-4 (Fig. 3C), while at week 41 IL-4 secretion increases as proliferation declines.

CD8 T-cell IFN-γ responses to HLA class I restricted peptides
Where possible we investigated CD8 T-cell IFN-γ production in response to characterised HLA class I restricted peptides (listed in Table 1), by ELISpot assay using cryopreserved PBMCs. As reported previously [15] Remune™ did not induce increases in CD8 T-cell responses. Although fluctuations occurred in CD8 T-cell IFN-γ responses these were not sustained and could not be attributed to ART or immunotherapy. Summary data is presented from week 0, following ART alone at week 16 and at week 65 in Table 2. Assays in which responses were not observed to the postive control, PHA, were considered to have failed, as denoted by "F". Of note is the observation that no patient in groups B, C or D demonstrated an increase in responses between week 16 and week 65. Patient 11 is an exception, although this patient had high baseline responses and by week 65 had discontinued ART causing considerable rebound viraemia, concomitant with strong HIV-1-specific lymphocyte proliferative responses as detailed above.

Discordant viraemia between patients receiving IL-2 with or without Remune™
Secondary to the main study protocol, further viral load and lymphocyte subset analysis was conducted at additional time points -week 18, week 22 and week 26 -for a sub-group of 15 patients receiving IL-2 in groups B (n = 9) and C (n = 6) on the last day of each IL-2 cycle. Small, transient elevations in HIV-1 RNA load were apparent on 12 occasions for 7 of 9 (78%) patients in group-B, and 2 of 6 patients (33%) in group-C. All these viral load elevations had spontaneously resolved by the next viral load test 3 weeks later at weeks 21, 25 and 29. The difference in occurrence of these viral load elevations remains evident when comparing the median viral loads for all the patients in groups B and C as shown in Fig. 1B and 1C.
The median viral load change (from 50 copies/ml) for the patients who had day 5 viral load measurements in group B were 23.5 copies/ml, 53 copies/ml and 0 copies/ml at the end of each IL-2 cycle. In comparison the median change in viral load for patients in group C who had day 5 viral load measurements was 0 at each time point. Change in viral load was not significantly different when comparing the sub-study patients in group B with those in group C, at any of the 3 individual IL-2 day 5 time points. However when taking all three day 5 time points together for each group, comparison between the two groups revealed a trend towards significance (p = 0.071, Pearson Chi-Squared).

Neutralising antibody responses in discordant virologic responders
As Remune™ displays the transmembrane (gp41) envelope antigen with strong neutralization epitopes [33][34][35], it may prime neutralizing antibodies to new epitopes. We tested the ability of plasma IgG from patients in Group C who did not experience day 5 viral blips to neutralize HIV-1 SF162 at weeks 0, 16 and 65. There was no effect of immunotherapy or ART on virus neutralization (data not shown).

Discussion
In this pilot study of combined immunotherapy with the therapeutic HIV-1 vaccine Remune™ and subcutaneous IL-2 in the context of ART, neither IL-2 nor Remune™ immunisation confered any substantial benefits to the effect of ART with regard to HIV-1-specific CD4 or CD8 T-cell responses, or neutralising antibodies. For the majority of these chronically HIV-1-infected patients responses to HIV-1 antigens remained negligible and there was little difference between the four immunotherapy arms. Possible reasons for this could be: the low CD4 T-cell counts of these patients when ART was initiated resulting in protracted immunosuppression and/or clonal dysfunction; a need for longer duration of ART before immunotherapeutic intervention, thus allowing greater immune recovery; the permanent depletion of HIV-1-specific CD4 T-cells by direct HIV-1 infection; and/or the timing of IL-2 therapy with immunisation which may have important consequences for induction or suppression of induced responses.
Previous Remune™ studies which induced proliferative responses comprised patients with higher pre-ART mean CD4 T-cell counts of 617 cells/μl [36] and 700 cells/μl blood [15]. The mean in this study was 303 cells/μl. 53% of these patients had CD4 nadirs below 300 cells/μl. Immune reconstitution in patients who initiate ART with low CD4 T-cell counts is impaired compared to those who initiate ART with higher CD4 T-cell counts [37,38]. The ability to respond to immunisation is also dependant on HIV-1-specific IL-4 production and lymphocyte proliferative responses Figure 3 HIV-1-specific IL-4 production and lymphocyte proliferative responses. Significant increases in CT.h4S delta cpm in response to HIV-1-specific IL-4 production were seen over the week 17-65 period (A) for groups B (ART + IL-2), C (ART + IL-2 + Remune™) and D (ART + Remune™), but not for group A (ART alone) (data not shown). Patient 11 is shown as an example of an inverse relationship between lymphocyte proliferative stimulation index (SI) (B) and IL-4 production as delta cpm (C) which was evident for 17 of 28 patients who were assessed for IL-4 production.  Peptides were identified from the NIH HIV Molecular Immunology Database website [50]. References for each peptide are also available at this website. RT (reverse transcriptase antigen), IN (integrase antigen). A HLA B35 is associated with rapid progression in HIV-1 infection. B HLA B57 is associated with slow/non progression in HIV-1 infection higher CD4 T-cell count nadirs and earlier initiation of ART [39].
The fate of missing HIV-1-specific CD4 T-cell responses is unclear. HIV-1 preferentially infects and deletes many HIV-1-specific CD4 T-cells [7], while some remain detectable, expressing IFN-γ, though unable to proliferate or express IL-2 [40,41]. The significant increase in HIV-1-specific IL-4 production from weeks 17 to 65 in group B (p24), C (p24) and D (gp120) could indicate clonal dysfunction in these patients. Only group A (ART alone) had no increase in HIV-1-specific IL-4 production. Thus immunotherapy in these patients appears to be associated with increasing levels of HIV-1-specific IL-4 production. IL-4, an anti-inflammatory type-2 cytokine, has a suppressive effect on lymphocyte proliferation [26,42]. The observation in a number of patients that HIV-1-specific IL-4 increases when proliferative responses diminish may indicate a mechanism by which clonal proliferation remains suppressed, although this needs further investigation. We previously found a balanced IL-4/IL-2 phenotype in HIV-1-specific CD4 T-cell responses in patients who remain disease free [27]. While IL-4 expression by HIV-1-specific CD4 T-cells may be thought of as a pathological anti-proliferative effect, it must be considered that this phenotype could be protective, by dampening immune activation and quashing viral replication. This relationship requires further investigation.
Despite the lack of induced HIV-1-specific T-cell responses in these patients we report significant increases in recall antigen proliferative responses, particularly for persistent antigens. These increases were largely evident between week 0 and 65 with no differences between groups, suggesting immunotherapy was ineffective in this respect. While some significant increases in proliferative responses to HIV-1 antigens were apparent from week 0 to 65 (group B and D), the same cannot be said regarding the immunotherapy period between weeks 17 and 65. Nor were there any significant differences in responses between groups. These results suggest that any improvements were singularly attributable to duration of ART.
Of note is one patient in group B, vaccinated with tetanus 4 weeks before receiving IL-2. High tetanus-specific proliferation was enhanced and sustained by subsequent IL-2, as reported separately [25]. In contrast a second patient received tetanus vaccination after IL-2 and did not respond. These responses may be dependent on administration of IL-2 subsequent to antigen priming, during Tcell contraction. Animal models demonstrate IL-2 administration during T-cell contraction enhances and prolongs responses, unlike co-administration of IL-2 with antigen when the survival of responding T cells is abrogated [24]. Our protocol and others that also achieved limited induc-tion of responses [43] utilized a co-administered model. Future trials will address such important issues.
We observed low-levels of transient self-limiting viraemia resulting from IL-2 therapy as previously reported [44]. Despite the lack of detectable cell-mediated responses induced by immunotherapy in these patients, the transient viral load blips we have reported appear to occur less in patients receiving IL-2 when administered with Remune™ in group C, with a trend towards significance (p = 0.071). Larger group sizes may have revealed a stronger relationship between Remune™ and protection from IL-2 induced transient viraemia, but this pilot study was not powered for such observations. This possible effect of Remune™ was not due to induction of neutralising antibodies, by the display of potentially sensitive epitopes on gp41 resulting from the removal of gp120 from Remune™ [45]. We have separately reported the induction of antibody responses against HLA-B62 and HLA-DR4 in some of these patients who received Remune™ immunisation [46], as Remune™ contains these antigens derived from the HUT-78 cell line in which it is grown. Group sizes are too small in this study to determine whether such responses may have played a role in potential protection from viral blips in group C.

Conclusion
Combined Remune™ and IL-2 with ART in advanced HIV-1 infection conferred no immunological benefits to ART. Taking together the absence of induced HIV-1-specific lymphocyte proliferative responses, CD8 T-cell IFN-γ responses and in vivo DTH responses these results imply that induction of renewed HIV-1-specific cell-mediated responses by therapeutic immunisation, even when supplemented with IL-2, is extremely problematic in patients who initiate ART with lower CD4 T-cell counts. Although a recently reported clinical trial of the vCP1433 canary pox-based therapeutic vaccine elicited p24-specific responses which were significantly associated with time off therapy in a subsequent treatment discontinuation protocol, these responses also remained transient, diminishing at study end [47]. This underscores the difficulties in inducing protective immune responses by therapeutic immunisation of chronically infected patients. Furthermore immunological protection in chronically infected individuals may be best conferred by autologous virus, as opposed to vaccine derived antigens as found with the vCP1452 canary pox vaccine [48] to which T-cell responses may in fact be associated with more rapid viral rebound following treatment interruptions [49]. In our study we saw the greatest proliferative responses to HIV-1 antigens in patients who experienced virological rebounds, demonstrating that autologous virus induces greater responses, albeit transiently, than immunisation or IL-2 therapy.
In these chronically infected treated patients, we found that immunotherapy was associated with increasing HIV-1-specific IL-4 production, which appears to negatively impact proliferative responses. HIV-1-specific IL-4 production may result from a general dysfunction of HIV-1specific CD4 T-cells with pathological implications for induction of HIV-1-specific responses. We suggest that these results underscore the importance of early initiation of ART. As Remune™ may have positive effects in less advanced patients [17], we suggest further investigations, with or without cytokine adjuvants, be conducted in patients for whom extensive immunological damage has been prevented with earlier initiation of ART.