Treatment of HIV-infected patients with highly active antiretroviral therapy (HAART) usually results in diminished viral replication, increasing CD4+ cell counts, a reversal of most immunological disturbances, and a reduction in risk of morbidity and mortality. However, approximately 20% of all HIV-infected patients do not achieve optimal immune reconstitution despite suppression of viral replication. These patients are referred to as immunological nonresponders (INRs). INRs present with severely altered immunological functions, including malfunction and diminished production of cells within lymphopoetic tissue, perturbed frequencies of immune regulators such as regulatory T cells and Th17 cells, and increased immune activation, immunosenescence, and apoptosis. Importantly, INRs have an increased risk of morbidity and mortality compared to HIV-infected patients with an optimal immune reconstitution. Additional treatment to HAART that may improve immune reconstitution has been investigated, but results thus far have proved disappointing. The reason for immunological nonresponse is incompletely understood. This paper summarizes the known and unknown factors regarding the incomplete immune reconstitution in HIV infection, including mechanisms, relevance for clinical care, and possible solutions.

T-allele homozygosity in rs6897932 is a predictor for faster CD4⁺ T-cell recovery after initiation of cART in HIV-infected whites, however, only in the first phase of immune recovery.

In the early days of the HIV epidemic, it was observed that a minority of the infected patients did not progress to AIDS or death and maintained stable CD4+ cell counts. As the technique for measuring viral load became available it was evident that some of these nonprogressors in addition to preserved CD4+ cell counts had very low or even undetectable viral replication. They were therefore termed controllers, while those with viral replication were termed long-term nonprogressors (LTNPs). Genetics and virology play a role in nonprogression, but does not provide a full explanation. Therefore, host differences in the immunological response have been proposed. Moreover, the immunological response can be divided into an immune homeostasis resistant to HIV and an immune response leading to viral control. Thus, non-progression in LTNP and controllers may be due to different immunological mechanisms. Understanding the lack of disease progression and the different interactions between HIV and the immune system could ideally teach us how to develop a functional cure for HIV infection. Here we review immunological features of controllers and LTNP, highlighting differences and clinical implications.

The aim of this study was to examine regulatory T cells (Tregs) in peripheral blood and liver tissue in patients with chronic hepatitis C virus (HCV) mono‐infection and in patients with HIV/HCV co‐infection. In a cross‐sectional study were included 51 patients with chronic HCV infection, 24 patients with HIV/HCV co‐infection and 24 healthy individuals. CD4+ and CD8+ Tregs were determined using flow cytometry. Fibrosis was examined by transient elastography. Inflammation, fibrosis and Tregs were determined in liver biopsies from 12 patients. Increased frequency of CD4+ and CD8+ Tregs was found in HIV/HCV co‐infected patients [median: 6.4% (IQR: 5.7–6.9) and 1.0% (0.7–1.2), respectively] compared to HCV mono‐infected patients [5.6% (4.2–6.3), P = 0.01 and 0.5% (0.3–0.7), P < 0.001, respectively]. Furthermore, HCV mono‐infected patients had increased frequencies of Tregs compared with healthy controls (P < 0.05). However, no associations between the frequency of Tregs and fibrosis were found. Furthermore, characterization of CD4+ Tregs using CD45RA demonstrated a higher frequency of activated Tregs in both HCV mono‐infected and HIV/HCV co‐infected patients compared with healthy controls. Finally, number of intrahepatic Tregs was associated with both peripheral CD8+ Tregs and intrahepatic inflammation. In conclusion, HCV mono‐infected patients and particularly HIV/HCV co‐infected patients have increased the frequency of CD4+ and CD8+ Tregs compared with healthy controls. Furthermore, CD4+ Tregs in infected patients displayed an active phenotype. Tregs were not associated with fibrosis, but a positive correlation between intrahepatic Tregs and inflammation was found. Taken together, these results suggest a role for Tregs in the pathogenesis of chronic HCV infection.