Risk of HIV Progression/Indications for ART

Background

The CD4 cell count and HIV viral load (RNA level) are closely linked to HIV-related illness and mortality, and are the laboratory measures that are followed in clinical practice. They are the primary markers that give prognostic information on disease progression and on response to antiretroviral therapy (ART) (see chapter CD4 and Viral Load Monitoring). However, it is increasingly recognized that a number of other factors are involved in HIV disease progression. These include individual HIV-specific immune responses, immune activation, viral factors, host genetics, and age. The role of these factors and their interplay is complex and incompletely understood.

CD4 Count

The CD4 count (and CD4 percentage) marks the degree of immunocompromise. The CD4 count is used to stage the patient's disease progression, determine the risk of opportunistic illnesses, and assess prognosis (see chapter CD4 and Viral Load Monitoring). The CD4 count also guides decision making about the urgency and the timing of ART initiation, helps in determining the need for prophylaxis against opportunistic infections, and helps in formulating differential diagnoses for symptomatic patients (see Table 1, Figure 1, and chapters CD4 and Viral Load Monitoring and Opportunistic Infection Prophylaxis).

Persons with HIV infection are at increased risk of complications at lower CD4 counts. A CD4 count of <200 cells/µL (or CD4 percentage of <14%) indicates severe immunosuppression, and is an AIDS-defining condition. Persons with CD4 counts below this level are at greater risk of a number of opportunistic illnesses and death, increasingly so at lower CD4 counts (see Table 1).

Increasing evidence suggests that the risk of complications from HIV infection occur across a broad spectrum of CD4 counts, and that patients with relatively high CD4 counts (those with counts of >350 cells/µL and even those with counts of >500 cells/µL) also have increased rates of morbidities compared with HIV-uninfected persons. The complications in persons with higher CD4 counts typically are not the classic AIDS-related opportunistic illnesses but are "non-AIDS" illnesses such as cardiovascular disease, neurocognitive decline, and non-AIDS-associated cancers.

In asymptomatic individuals, CD4 count has typically been the main indicator of need for ART. It is well established that ART is extremely effective at reducing HIV-related illness in persons with lower CD4 counts. In recent years, accumulating data have suggested that ART may be beneficial even for persons with higher pretreatment CD4 counts.

Randomized trials have shown that starting ART for asymptomatic patients with pretreatment CD4 counts of 200-350 cells/µL results in decreased morbidity and mortality compared with starting therapy for persons with CD4 counts of <200 cells/µL. For patients with pretreatment CD4 counts of >350 cells/µL, data from two randomized controlled studies and several cohort studies have found decreased rates of complications and death among persons who initiated ART at CD4 counts of ≥350 cells/µL, compared with persons who initiated treatment at lower CD4 counts. Additionally, some (though not all) observational evidence suggests a mortality benefit of ART even among persons with pretreatment CD4 counts of >500 cells/µL. These cohort studies are complemented by a number of investigations that demonstrate ongoing and adverse effects of HIV and associated inflammation on various organ systems.

These lines of evidence, along with studies showing a substantial impact of ART in decreasing HIV transmission, and the availability of ARVs that generally are safe, tolerable, and effective, support the rationale for earlier initiation of treatment. The current U.S. Department of Health and Human Services (DHHS) adult and adolescent treatment guidelines recommend starting ART for all HIV-infected persons regardless of CD4 count. The strength of this recommendation is greater if the CD4 count is lower or the clinical status is poorer (see Table 2 and chapter Antiretroviral Therapy).

HIV Viral Load

Whereas the CD4 count is an indicator of immune system function, the HIV viral load (RNA level) gives prognostic information on how quickly the CD4 count is likely to decline and, consequently, the risk of disease progression. Patients with high HIV viral loads generally demonstrate a faster decline in CD4 count and progression to AIDS-related illnesses; they also may have a higher rate of non-AIDS-related events even with relatively high CD4 counts (e.g., >350 cells/µ). Those with low viral loads will usually have higher CD4 counts and remain asymptomatic for prolonged periods. A small percentage of persons with HIV infection may have very low or undetectable viral loads for extended periods of time.

By themselves, CD4 count and HIV viral load are useful, albeit rough, prognostic indicators. When considered together, they constitute a finer tool to estimate the risk of progression (see Figure 1).

Other Factors Associated with HIV Progression

Although the CD4 count and HIV viral load are the most important predictors of HIV progression, it is increasingly recognized that a number of other factors, and likely others that remain unknown, contribute to disease progression in HIV infection.

Viral factors

Variations in the HIV genome have been associated with an altered rate of disease progression. For example, deletions in the nef gene have been associated with a slow rate of progression. On the other hand, virus that uses the CXCR4 protein as a coreceptor for entry (termed X4 virus or syncytia-inducing virus) has been associated with accelerated progression. As another example, drug-resistance mutations may affect how efficiently the virus replicates (viral fitness). Patients who have virus with decreased fitness have slower immune deterioration than those with wild-type virus.

Host immune factors

Host genetic factors have been shown to alter the rate of HIV progression. Various human leukocyte antigen (HLA) alleles have been associated with faster or slower progression rates. Genetic polymorphisms also play a role. For example, CCR5 is a chemokine receptor that can serve as a coreceptor for HIV entry into the CD4 cell. A naturally occurring variant allele for CCR5 has a 32 base pair deletion. Individuals who are heterozygous for this allele have slower progression of HIV disease.

Increased immune activation and elevated markers of inflammation, such as IL-6 and D-dimer, also have been associated with risk of disease progression and death. They also may be involved in the ongoing damage seen in a number of end organs. Although T-cell activation and levels of inflammation decrease with ART, they often do not return to normal.

Age

Several studies have shown a higher risk of morbidity and mortality in older patients. When followed from seroconversion, older patients demonstrate faster disease progression compared with younger patients (see Table 3). Older patients also are found to have a less robust increase in the CD4 count in response to ARTand may have a higher rate of non-AIDS-related morbidities. These observations have led to the current DHHS recommendation to initiate ART in all HIV-infected individuals over age 50, regardless of CD4 count.

Patient Education

• The CD4 cell count and HIV viral load are the two markers that provide information on the degree of current immunocompromise and the risk of disease progression.
• The lower the CD4 count, the higher the risk of AIDS-related illness.
• Current United States guidelines recommend ART for all HIV-infected individuals. In areas where treatment resources are limited, the CD4 count is the major indicator for initiation of ART.
• A low HIV viral load is associated with slower immune deterioration; a high viral load is associated with quicker immune deterioration.
• Older individuals may have a poorer response to therapy; earlier initiation of therapy may be considered for older patients.

References

• Cohen MS, Chen YQ, McCauley M, et al.; HPTN 052 Study Team. Prevention of HIV-1 infection with early antiretroviral therapy. N Engl J Med. 2011 Aug 11;365(6):493-505.
• Collaboration of Observational HIV Epidemiological Research Europe (COHERE) Study Group. Response to combination antiretroviral therapy: variation by age. AIDS. 2008 Jul 31;22(12):1463-73.
• Concerted Action on Sero-Conversion to AIDS and Death in Europe. Time from HIV-1 seroconversion to AIDS and death before widespread use of highly-active antiretroviral therapy: a collaborative re-analysis. Collaborative Group on AIDS Incubation and HIV Survival including the CASCADE EU Concerted Action. Lancet. 2000 Apr 1;355(9210):1131-7.
• Connor RI, Sheridan KE, Ceradini D, et al. Change in coreceptor use coreceptor use correlates with disease progression in HIV-1-infected individuals. J Exp Med. 1997 Feb 17;185(4):621-8.
• Deeks SG, Wrin T, Liegler T, et al. Virologic and immunologic consequences of discontinuing combination antiretroviral drug therapy in HIV-infected patients with detectable viremia. N Engl J Med. 2001 Feb 15;344(7):472-80.
• Egger M, May M, Chene G, et al. Prognosis of HIV-1-infected patients starting highly active antiretroviral therapy: a collaborative analysis of prospective studies. Lancet. 2002 Jul 13;360(9327):119-29.
• European AIDS Clinical Society. Clinical Management and Treatment of HIV-Infected Adults in Europe. English Version 5; November 2009.
• Kirchhoff F, Greenough TC, Brettler DB, et al. Brief report: absence of intact nef sequences in a long-term survivor with nonprogressive HIV-1 infection. N Engl J Med. 1995 Jan 26;332(4):228-32.
• Kuller L, SMART Study Group. Elevated levels of interleukin-6 and D-dimer are associated with an increased risk of death in patients with HIV. In: Program and Abstracts of the 15th Conference on Retroviruses and Opportunistic Infections; Boston; February 3-6, 2008. Abstract 139.
• Lederman MM, Rodriquez B, Sieg S. Immunopathogenesis of HIV Infection. In: Coffey S, Volberding PA, eds. HIV InSite Knowledge Base [online textbook]. San Francisco: UCSF Center for HIV Information; January 2006.
• Mellors JW, Rinaldo CR Jr, Gupta P, et al. Prognosis in HIV-1 infection predicted by the quantity of virus in plasma. Science. 1996;272:1167-70.
• Reekie J, Gatell JM, Yust I, et al.; EuroSIDA in EuroCoord. Fatal and nonfatal AIDS and non-AIDS events in HIV-1-positive individuals with high CD4 cell counts according to viral load strata. AIDS. 2011 Nov 28;25(18):2259-68.
• Rodríguez B, Sethi AK, Cheruvu VK, et al. Predictive value of plasma HIV RNA level on rate of CD4 T-cell decline in untreated HIV infection. JAMA. 2006 Sep 27;296(12):1498-506.
• Sterne JA, May M, Costagliola D, et al; When to Start Consortium. Timing of initiation of antiretroviral therapy in AIDS-free HIV-1-infected patients: a collaborative analysis of 18 HIV cohort studies. Lancet. 2009 Apr 18;373(9672):1352-63.
• U.S. Department of Health and Human Services. Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents. March 27, 2012.