Chronic immunodeficiency virus infections are characterized by dysfunctional cellular and humoral antiviral immune responses. As such, immune modulatory therapies that enhance and/or restore the function of virus-specific immunity may protect from disease progression. Here, we investigate the safety and immune restoration potential of the blockade of co-inhibitory receptor programmed death-1 (PD-1) during chronic SIV infection in macaques. We demonstrate that PD-1 blockade using an antibody to PD-1 is well tolerated and results in rapid expansion of virus-specific CD8 T cells with improved functional quality. This enhanced T cell immunity was seen in the blood and also in the gut, a major reservoir of SIV infection. PD-1 blockade also resulted in proliferation of memory B cells and increases in SIV envelope-specific antibody. These improved immune responses were associated with significant reductions in plasma viral load and also prolonged the survival of SIV-infected macaques. Impressively, blockade was effective during the early (wk10) as well as late (∼wk90) phases of chronic infection even under conditions of severe lymphopenia. These results demonstrate enhancement of both cellular and humoral immune responses during a pathogenic immunodeficiency virus infection by blocking a single inhibitory pathway and identify a novel therapeutic approach for HIV/AIDS.

IntroductionA profound impairment of immune functions occurs in individuals infected with human immunodeficiency virus type 1 (HIV-1). Both the cellular and the humoral arms of the immune system are unable to control the infection, which ultimately results in severe exhaustion of several lymphocyte functions and increased susceptibility to secondary and opportunistic infections. Major immunologic defects occur in the B-cell compartment. 1 Polyclonal B-cell activation is demonstrated by hypergammaglobulinemia and spontaneous antibodies' (Abs) production by cultured peripheral lymphocytes 2,3 ; additional signs of B-cell abnormality are the high incidence of B-cell tumors 4 and the deregulated expression of several surface molecules like Fas, Fas ligand (FasL), CD5, CD21, and CD27. 5-8 B-cell hyperactivity is also accompanied by functional defects since humoral immune responses following immunization are severely impaired in HIV-1-infected subjects and B lymphocytes from patients are poorly responsive to in vitro stimulation. [9][10][11] Several mechanisms may account for the B-cell abnormalities in HIV-1 infection. A direct effect of virus replication or viral proteins on B-cell function has been shown 12 and sustained by the observation that polyclonal B-cell activation is strongly reduced following effective antiretroviral treatment. 13-15 HIV-driven unbalanced production of several cytokines like tumor necrosis factor ␣ (TNF-␣), interleukin 6 (IL-6), IL-10, and IL-15 has also been involved in B-cell dysfunctions. [16][17][18] Defective T-cell help may account for B-cell unresponsiveness to T-cell-dependent antigens. 19,20 The defect of B cells in HIV-1 infection appears, however, to be intrinsic since it begins early during infection preceding functional and quantitative defects in T-helper activity and cannot be restored by allogenic normal CD4 ϩ T cells in vitro. 3,21 The mechanisms inducing hypergammaglobulinemia in HIV-1 infection are only partially known. Activation driven by CD4 ϩ T cells, monocytes, and natural killer (NK) cells through CD40-CD40 ligand (CD40L) interaction and an inappropriate cytokine supply may have a relevant role in inducing abnormal differentiation of B cells. 17,22 In addition, HIV-1 itself may directly affect B-cell activation and dysfunction, inducing the appearance of a subset of CD21 Ϫ B cells which have been proposed to contribute to increased antibody production. 23,24 A recent work by Hunziker et al 25 has suggested that naive B cells represent an important source of hypergammaglobulinemia and autoantibody production in chronic viral infections.Because of the lack of protective humoral immunity, HIV-1-infected individuals receive vaccination against several pathogens. However, many studies have reported an impaired humoral immune response in most of the patients after vaccination. [9][10][11]26,27 From the Microbiology and Tumor Biology Center, Karolinska Institutet, and the Gay Men's Health Clinic, The Soder Hospital, Stockholm, Sweden; the Swedish Institute for Infectious...

Circulating memory B cells are severely reduced in the peripheral blood of HIV-1-infected patients. We investigated whether dysfunctional serologic memory to non-HIV antigens is related to disease progression by evaluating the frequency of memory B cells, plasma IgG, plasma levels of antibodies to measles, and Streptococcus pneumoniae, and enumerating measles-specific antibody-secreting cells in patients with primary, chronic, and long-term nonprogressive HIV-1 infection. We also evaluated the in vitro production of IgM and IgG antibodies against measles and S pneumoniae antigens following polyclonal activation of peripheral blood mononuclear cells (PBMCs) from patients. The percentage of memory B cells correlated with CD4 ؉ T-cell counts in patients, thus representing a marker of disease progression. While patients with primary and chronic infection had severe defects in serologic memory, long-term nonprogressors had memory B-cell frequency and levels of antigen-specific antibodies comparable with controls. We also evaluated the effect of antiretroviral therapy on these serologic memory defects and found that antiretroviral therapy did not restore serologic memory in primary or in chronic infection. We suggest that HIV infection impairs maintenance of long-term serologic immunity to HIV-1-unrelated antigens and this defect is initi- IntroductionThe ability to maintain an intact memory B-cell compartment is an essential component of the immune response to (re-) infections. 1 Maintenance of serologic memory is carried out by plasma cells and memory B cells [1][2][3] ; memory B cells play an essential role in the maintenance of antibody (Ab) levels by rapidly generating secondary immune responses upon reinfection or antigenic stimulation. 4 One of the most deleterious effects of HIV-1 infection is B-lymphocyte hyperactivation, which manifests as hypergammaglobulinemia, increased expression of activation markers, high spontaneous Ab production in vitro, and increased incidence of B-cell lymphomas. 5 Paradoxically, HIV-1-infected persons, especially those in advanced stages of disease, also have impaired humoral immune response to vaccination, and their B cells respond poorly to in vitro stimulation by common mitogens such as SAC and PWM. 5 Earlier studies suggest that naive and memory B cells differentially contribute to B-cell dysfunctions in HIV-1 infection. [6][7][8][9][10] Circulating memory B cells in peripheral blood from patients with chronic HIV-1 infection (CHI) are severely reduced and die by apoptosis. 6,11 Serum Abs against measles, tetanus toxoid, and HIV-1 antigens are significantly reduced in patients with low memory B cells, indicating that this phenotypic alteration may severely affect memory B-cell functions. 10 Recently, we reported that during primary HIV-1 infection (PHI), memory B cells are phenotypically and functionally altered though not significantly reduced in number. 12 These alterations were only partially recovered upon antiretroviral therapy (ART), suggesting that PHI sets the stage ...

Rapid progression to AIDS is a significant problem, especially in developing countries, where the majority of HIV-infected individuals reside. As rapid disease progression is also frequently observed in SIV-infected macaques, they represent a valuable tool to investigate the pathogenesis of this condition in humans. Here, we have shown that pathogenic SIV infection in rhesus macaques resulted in a rapid depletion (as early as week 2) of activated memory B (CD21 -CD27 + ; mB Act ) cells that was strongly associated with rapid disease progression.