Prolonged Posttreatment Virologic Control and Complete Seroreversion After Advanced Human Immunodeficiency Virus-1 Infection

Recent advances in CD8+ T cell-based immune therapies for HIV cure

Achieving a cure for HIV infection is a global priority. There is substantial evidence supporting a central role for CD8⁺ T cells in the natural control of HIV, suggesting the rationale that these cells may be exploited to achieve remission or cure of this infection. In this work, we review the major challenges for achieving an HIV cure, the models of HIV remission, and the mechanisms of HIV control mediated by CD8⁺ T cells. In addition, we discuss strategies based on this cell population that could be used in the search for an HIV cure. Finally, we analyze the current challenges and perspectives to translate this basic knowledge toward scalable HIV cure strategies.

Elite and posttreatment controllers, two facets of HIV control

PURPOSE OF REVIEW

The quest for HIV-1 cure could take advantage of the study of rare individuals that control viral replication spontaneously (elite controllers) or after an initial course of antiretroviral therapy (posttreatment controllers, PTCs). In this review, we will compare back-to-back the immunological and virological features underlying viral suppression in elite controllers and PTCs, and explore their possible contributions to the HIV-1 cure research.

RECENT FINDINGS

HIV-1 control in elite controllers shows hallmarks of an effective antiviral response, favored by genetic background and possibly associated to residual immune activation. The immune pressure in elite controllers might select against actively transcribing intact proviruses, allowing the persistence of a small and poorly inducible reservoir. Evidence on PTCs is less abundant but preliminary data suggest that antiviral immune responses may be less pronounced. Therefore, these patients may rely on distinct mechanisms, not completely elucidated to date, suppressing HIV-1 transcription and replication.

SUMMARY

PTCs and elite controllers may control HIV replication using distinct pathways, the elucidation of which may contribute to design future interventional strategies aiming to achieve a functional cure.

Why the HIV Reservoir Never Runs Dry: Clonal Expansion and the Characteristics of HIV-Infected Cells Challenge Strategies to Cure and Control HIV Infection

Antiretroviral therapy (ART) effectively reduces cycles of viral replication but does not target proviral populations in cells that persist for prolonged periods and that can undergo clonal expansion. Consequently, chronic human immunodeficiency virus (HIV) infection is sustained during ART by a reservoir of long-lived latently infected cells and their progeny. This proviral landscape undergoes change over time on ART. One of the forces driving change in the landscape is the clonal expansion of infected CD4 T cells, which presents a key obstacle to HIV eradication. Potential mechanisms of clonal expansion include general immune activation, antigenic stimulation, homeostatic proliferation, and provirus-driven clonal expansion, each of which likely contributes in varying, and largely unmeasured, amounts to maintaining the reservoir. The role of clinical events, such as infections or neoplasms, in driving these mechanisms remains uncertain, but characterizing these forces may shed light on approaches to effectively eradicate HIV. A limited number of individuals have been cured of HIV infection in the setting of bone marrow transplant; information from these and other studies may identify the means to eradicate or control the virus without ART. In this review, we describe the mechanisms of HIV-1 persistence and clonal expansion, along with the attempts to modify these factors as part of reservoir reduction and cure strategies.

Serum IgG1 and IgG4 could contribute to partial control of viral rebound in chronically HIV-1-infected patients

OBJECTIVES

Few studies have investigated chronically infected individuals after antiretroviral therapy (ART) interruption (ATI, analytical therapy interruption); thus, we investigated the association between some HIV-specific antibodies and viral control.

DESIGN

All enrolled patients were previously described in the APACHE study. Briefly, the study was conducted on HIV-1 chronically infected patients, with HIV-RNA less than 50 copies/ml for at least 10 years, CD4+ cell count greater than 500 cells/μl and HIV-DNA less than 100 copies/106 PBMC. The ART regimen in use at the time of ATI was resumed at confirmed viral rebound (CVR, defined as two consecutive HIV-RNA >50 copies/ml).

METHODS

Collection of sera and analysis of both binding antibodies (BAbs) and neutralizing antibodies (NAbs) was performed at three different time points: ATI, CVR and time of viral re-suppression after ART resumption.

RESULTS

IgG subclasses (IgG1, IgG2, IgG3 and IgG4) from the four patients with highest levels of neutralization were found to block viral infection. All patients had CVR after ATI at a median time of 21 days (14-56). After ART resumption, all the enrolled patients achieved HIV-RNA less than 50 copies/ml in 42 days (21-98). We observed a strong increase of either BAbs and NAbs titers from ATI to viral re-suppression in one patient, who showed the longest period of virus undetectability during ATI. In this patient, BAbs and NAbs specifically belonged to both IgG1 and IgG4 subclasses, directed to env antigen.

CONCLUSION

env-specific NAbs and BAbs belonging to IgG1, IgG4 subclasses could be helpful to monitor long-term responses able to control virus replication and eradicate HIV infection.

How elite controllers and posttreatment controllers inform our search for an HIV-1 cure

A small percentage of people living with HIV-1 can control viral replication without antiretroviral therapy (ART). These patients are called elite controllers (ECs) if they are able to maintain viral suppression without initiating ART and posttreatment controllers (PTCs) if they control HIV replication after ART has been discontinued. Both types of controllers may serve as a model of a functional cure for HIV-1 but the mechanisms responsible for viral control have not been fully elucidated. In this review, we highlight key lessons that have been learned so far in the study of ECs and PTCs and their implications for HIV cure research.