Two novel immune therapies in early investigation: autologous dendritic cells and CD4 zeta gene-modified T cells

Immune cells extracted from individuals and then modified to enhance the individual immune response to HIV infection, appear to be a safe and feasible approach to HIV treatment, according to several reports this week at the XVII International AIDS Conference.

In a poster discussion on Tuesday afternoon, investigators presented data on several immune therapies in early investigational stages of development. Two of these techniques were based on autologous immune cells (i.e., immune cells obtained from each individual patient.

Jean-Pierre Routy of McGill University Health Centre, Montréal, Canada, presented feasibility and safety data on a novel agent based on autologous (i.e., the patient's own) dendritic cells. Dendritic cells are antigen-presenting cells: they display recognisable portions of infectious organisms to other cells of the immune system. In this study, dendritic cells from each individual patient were "primed" with RNA from the same patient's own HIV. The hope is that the resultant product (known as AGS-004 and trade named Arcelis) could act as a "personalised immunotherapy", enhancing CD8-specific responses to HIV, and helping to surmount the variability that allows HIV to elude the body's immune response.

The primary study objectives were to assess the feasibility of the manufacturing process, and to obtain preliminary safety profiles in human subjects. Study participants were ten HIV-positive individuals on successful antiretroviral therapy, with HIV viral load suppressed to below 40 copies/ml and CD4 cell counts ≥ 350 cells/mm³ (median, 415 cells/mm³).

In the first step of the production process, dendritic cells (DCs) were extracted from whole blood samples taken from the participants. The next step utilised stored samples of infectious plasma obtained from the same patient prior to antiretroviral treatment, when significant amounts of HIV were still present. Specific segments of HIV RNA were obtained from the archived plasma. These RNA segments were those which coded for HIV antigens gag, nef, rev, and vpr – distinctive pieces of HIV proteins which the immune system can recognise and respond to.

These autologous HIV RNA segments were then introduced into the patient's dendritic cells (by a process known as electroporation), along with RNA that codes for a cellular messenger molecule (CD40L) that boosts interaction between dendritic and CD8+ cells. This resulted in modified cells which should, theoretically, express greater quantities of HIV antigens than the patient's immune system would otherwise be able to do.

The resultant product was administered as four intradermal injections of 0.6 ml, each consisting of 1.2x10⁷ modified dendritic cells. Injections were given monthly in addition to the patients' ongoing antiretroviral therapy. Follow-up continued to a maximum of twelve months.

The AGS-004 modified dendritic cells were successfully generated from all ten patients, and all of the participants completed the study treatment. Adverse events were mild (grade 1 or absent) and included flu-like and gastrointestinal symptoms, fatigue, and injection site reactions. None of the subjects developed increases ("blips") in HIV viral load, or evidence of developing any autoimmune responses. No significant changes in either absolute CD4 or CD8 cell counts were seen.

Response was measured as the increase in the capacity of CD8 cells to proliferate in response to dendritic cell targets containing the four HIV antigens (Gag, Vpr, Rev and Nef). A significant increase in proliferative response (at least double the baseline value) was noted in four of the ten subjects, and a partial response (significant increase above untreated controls) in a further three. As expected, these responses were specific for the four HIV antigens selected. As intended, there was no significant increase in CD4 cell immune response.

Interestingly, patients treated with antiretroviral therapy early in the course of their infection (within six months) showed a trend towards more robust antiviral immune responses compared to those in whom therapy was started six months or more post infection.

Dr. Routy concluded that these Phase I data "demonstrated the feasibility, safety, and immunogenicity of AGS-004 treatment in ART controlled subjects" and support the implementation of a Phase II multi-centre study. Such a study is already ongoing in Canadian centres.

Ultimately, AGS-004 is meant to be investigated as a means of controlling viral load while interrupting antiretroviral therapy. Importantly, Dr. Routy called for the creation of an expert panel to produce a consensus recommendation on the ethical considerations of any clinical trials involving such treatment interruptions.

Naomi Aronson presented data on another novel investigational approach on behalf of researchers from the Walter Reed Army Institute of Research, Washington, US. This approach, based on a similar therapy used in cancer treatment and building on previous work by Bruce Walker, Stephen Deeks and others, involves genetically modifying T-cells to include a marker normally found only on CD4 cells.

CD4 cells are a subset of the larger group of T-cells, which play various roles in the human immune response to infection. CD4 cells are uniquely identified by the CD4 protein molecule which appears on the cell surface. This CD4 protein also serves as a target by which HIV attaches to and infects the cell.

One particular segment ("domain") of the CD4 molecule, known as CD4ζ ("CD4 zeta"), also serves to initiate a chain of immune response processes within the cell when triggered by infectious antigens. The investigators hypothesised that, by displaying the CD4ζ marker on a larger repertoire of T-cells, the immune response to HIV infection might be heightened. The basic method of this study was, therefore, to introduce the CD4ζ gene into a wider range of T-cells, inducing the resultant "CD4ζ gene-modified T lymphocytes" to produce the CD4ζ surface protein.

This preliminary study was a randomised, laboratory-blinded, clinical trial with three treatment arms. In Arm 1, participants received 1.2 MIU/m²/day subcutaneous for 56 days (the IL-2 arm). (Also see the aidsmap report from the International AIDS Conference on IL-2 here.) In Arm 2, they received an infusion of autologous, CD4ζ gene-modified T lymphocytes (the CD4ζ arm). Patients in Arm 3 received both treatments.

Fifteen HIV-positive adults on successful antiretroviral treatment were enrolled and randomised, five to each study arm. All had HIV viral loads less than 50 copies/ml and a nadir (lowest-ever) CD4 cell count no lower than 200 cells/³; the group was 87% male, 53% white and 27% black, with a median age of 37 years and median baseline CD4 count 775 cells/mm³.

Rectal lymphoid tissue was biopsied at baseline, two, six, and 52 weeks. Since HIV viral load was undetectable in all participants, the extent of the bodily HIV reservoir was estimated by RT-PCR measurement of HIV DNA and of RNA from peripheral blood mononuclear cells (PBMC) and from rectal lymphoid tissue (RLT).

In the study arms including CD4ζ treatment (Arms 2 and 3), participants were injected with a mean of 6.2x10⁹ viable modified cells. Median changes in CD4 cell count from baseline to 4 and 52 weeks respectively were -50 and -15 in Arm 1 (IL-2), -2 and +52 in Arm 2 (CD4ζ) and +422 and +93 in Arm 3 (dual treatment) (p=.02).

There were limited study-related adverse events. There was a suggestion that the total size of the bodily HIV reservoir (as measured by HIV DNA levels in PBMCs) decreased from baseline to one year in the CD4ζ-containing treatment arms, but the finding was not statistically significant. RNA and DNA from the gene-modified cells was found in both PBMCs and rectal lymphoid tissue, and were seen to persist after one year, indicating that the cells had migrated into lymphoid (immune) tissue and persisted there.

Observations were limited by the small number of patients and the variability between them. However, Dr. Aronson concluded that both the IL-2 and CD4ζ treatments were well tolerated, that the increase in CD4 counts in Arm 3 suggests a strategy for immune reconstitution in patients with poor CD4 recovery on antiretrovirals, and that these findings provided a rationale for further study of this immune treatment strategy.