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ARTICLE

HIV combination therapy: partial immune restitution unmasking latent cryptococcal infection

Woods, Marion L. II1,2; MacGinley, Robert1; Eisen, Damon P.1; Allworth, Anthony M.1

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Abstract

Introduction

Successful antiretroviral combination therapy can produce prompt and sustained reduction of viral load and subsequent recovery of CD4 cell numbers in HIV-infected patients [1,2]. One would expect a concomitant recovery of immune function as HIV viral load reduction is achieved. We have observed two cases of cryptococcal meningitis and one re-exacerbation of cryptococcal antigen-associated meningitis diagnosed within 1–6 weeks of initiation of highly active antiretroviral combination therapy (HAART). We hypothesize that partial restoration of cell-mediated immunity induced by effective HIV therapy facilitated development of sufficient inflammatory responses in the central nervous system to produce symptoms and signs in patients who were latently infected with Cryptococcus (two patients). We believe that the third patient developed clinically symptomatic meningitis (following successful therapy for cryptococcal meningitis) in response to residual cryptococcal antigen in the cerebrospinal fluid (CSF) following partial immune restitution produced by HAART.

Materials and methods

Patients identified in this report were admitted to the Royal Brisbane Hospital Infectious Diseases Unit between 1 January 1996 and 31 December 1996. The Infectious Diseases Unit at the Royal Brisbane Hospital provides primary ambulatory and inpatient care for approximately 200 HIV-infected patients on a regular basis each year, in addition to consulting with the AIDS Medical Unit, which provided ambulatory care for approximately 200 HIV-infected patients in the Brisbane area. In 1996, our primary patients had CD4 cell counts with the following distributions: < 50 × 106/l (15%), 50–100 × 106/l (9.5%), 101–199 × 106/l (16.4%), > 200 × 106/l (58.9%). All culture-proven cases of cryptococcal meningitis were included. The following brief case descriptions outline the temporal association of antiretroviral combination therapy with development of clinically apparent meningitis associated with Cryptococcus.

Results

Patient 1 was diagnosed 7 years previously with HIV infection and was relatively asymptomatic (CD4 cells 5 × 106/l). He commenced antiretroviral combination therapy consisting of saquinavir 600 mg three times daily, lamivudine 150 mg twice daily and stavudine 40 mg twice daily. He had not previously taken anti-retroviral agents (Table 1). Four days after commencing combination therapy, he developed bilateral eye pain, and frontal headaches that were worse at night and intensified by coughing. He also experienced nausea/vomiting, photophobia, neck stiffness, and fever and sweats during the brief prodrome prior to diagnosis. CSF examination revealed a leukocyte count of 14 × 103/l (40% polymorphonuclear, 60% mononuclear), at least three encapsulated yeast cells, glucose 2.7 mmol/l, and protein 452 mg/l. Cryptococcus neoformans var. neoformans was isolated from CSF and blood. Pretreatment HIV viral load was 2.3 × 106 copies/ml, which decreased to less that 200 copies/ml within 1 month of starting therapy (Table 1).

Table 1
Table 1:
. Summary of characteristics of the three HIV-infected patients who developed clinically apparent meningitis after starting highly active antiretroviral combination therapy.

Patient 2 had been known to be HIV-positive for 7 years (CD4 cells 30 × 106/l) and was admitted for control of lateral chest pain secondary to an exacerbation of post-herpetic neuralgia. His antiretroviral regimen had been recently altered to include lamivudine 150 mg twice daily (begun at 39 days prior to diagnosis), stavudine 40 mg twice daily (begun at 15 days prior to diagnosis), in addition to saquinavir 600 mg three times daily. Five days after admission, the patient developed severe frontal headaches lasting 3 days.

Computed tomography scan revealed cerebral atrophy and basal ganglia calcifications without mass lesions or contrast enhancement. CSF examination revealed a leukocyte count of 3 × 103/l, numerous encapsulated yeast cells, glucose 3.2 mmol/l, protein 532 mg/l, and opening pressure of 28 cm H2O (Table 1). C. neoformans var. neoformans was isolated from the CSF (blood not cultured).

Patient 3 (CD4 cell count 40 × 106/l) presented with Pneumocystis carinii pneumonia (PCP) and cryptococcal meningitis as his AIDS-defining illnesses. The initial CSF examination revealed a leukocyte count of 9 × 103/l, glucose 2.2 mmol/l, and protein 980 mg/l. C. neoformans var. neoformans was isolated from the CSF and blood. One month after completing successful therapy for PCP with oral trimethoprim-sulphamethoxazole and amphotericin B (0.7 mg/kg for 3 weeks) followed by itraconazole 400 mg daily for cryptococcal meningitis, the patient was commenced on saquinavir 600 mg three times daily, lamivudine 150 mg twice daily, and zidovudine 250 mg twice daily. Ten days after the commencement of combination antiretroviral therapy, he developed fever and a stiff neck, which were confirmed the following day. CSF examination revealed a lymphocyte count of 1 × 105/l, glucose 2.6 mmol/l, and protein 1055 mg/l (Table 1). CSF cultures were negative for Cryptococcus, mycobacteria, bacteria and viruses. Enteroviral cultures from nasopharyngeal washes and stool samples were also negative. Cryptococcal antigen was present at a titre of 200 in the CSF. Pretreatment HIV viral load was 4.8 × 105 copies/ml and 6 weeks later the viral load was 1.3 × 103 copies/ml. Therapy was not altered and the patient's meningeal symptoms and signs resolved over 2 weeks.

Discussion

Two patients with advanced HIV infection were diagnosed with cryptococcal meningitis within 7–39 days of starting or altering antiretroviral therapy, which included at least two or more antiretroviral agents. A third patient, who had been successfully treated for simultaneous PCP and cryptococcal meningitis in the previous month, was diagnosed with meningitis (associated with the presence of cryptococcal antigen) 11 days after initiating antiretroviral combination therapy.

Although it is possible that the temporal association of commencement of HAART with cases 1 and 2 reflect chance occurrences, and that case 3 represents drug-related aseptic meningitis (treatment was not altered, no other pathogen was identified), we suggest that partial immune restitution led to the diagnosis of clinically apparent Cryptococcus-associated meningitis in each patient. For example, all patients had significant and sustained elevation of CD4 cell numbers following effective antiretroviral therapy. Patients 1 and 3 exhibited significant reduction in HIV viral load when measured 4 and 6 weeks, respectively, after initiation of combination therapy. Patients 1 and 3 had inflammatory cell reactions in the CSF, which were in keeping with cellular responses described in non-HIV-associated cryptococcal meningitis [3]. In case 3, we hypothesize that antiretroviral combination therapy enhanced the immune response to residual CSF cryptococcal antigen, which led to meningeal symptoms and signs.

A recent clinical epidemiological study of 171 cryptococcal meningitis patients found that non-immunosup-pressed patients were significantly more likely than AIDS patients to have a stiff neck (75 versus 33%; P < 0.01) and leukocyte counts above 1 × 104/l in CSF (92 versus 45%; P < 0.01), although the overlap between the two groups was large [3]. The meningitis patients in our report exhibited clinical signs and CSF findings that were comparable to the non-immuno-compromised group of patients described in the above study, with two out of three of our patients presenting with neck stiffness and CSF leukocyte counts above 1 × 104/l, consistent with partial immune restitution. Although patient 3 had sterile CSF at the time of reexacebation of meningitis, the presence of CSF cryptococcal antigen, which can stimulate delayed-type hypersensitivity [4] as well as induce proinflammatory cytokines [5], in the context of a partially reconstituted immune response, may have been the trigger for clinically apparent meningitis.

Therapy for a number of infectious diseases are known to induce enhancement of cell-mediated immunity, which paradoxically worsens the clinical outcome. Examples of this paradoxical effect are well-recognized features that can occur during the treatment of leprosy [6–8], tuberculous meningitis [9–11], and PCP [12]. The pathology of immune enhancement during leprosy (reversal reactions and erythema nodosum leprosum) is associated with increased numbers of CD4 cells, and increased levels of interferon-γ and interleukin (IL)-2, all of which are indicative of enhanced cell-mediated immunity [6]. All three of our patients had clinically relevant increases in CD4 cell counts following institution of HIV combination therapy, which may have contributed to partial immune restitution.

A recent report [13] describing five cases of cytomegalovirus (CMV) retinitis occurring within 4–7 weeks of commencing effective antiretroviral combination therapy in AIDS patients with CD4 cell counts below 85 × 106/l is consistent with our hypothesis. All five of the CMV retinitis patients in that report developed disease associated with partial immune recovery evidenced by significant increases in CD4 cell counts [13]. Furthermore, Race et al. [14] have reported severe lymphadentitis associated with Mycobacterium avium complex occurring 6–20 days (median, 8.5 days; mean, 11.3 days) after commencement of HAART (indinavir plus zidovudine, lamivudine or stavudine, or didanosine) in five patients with advanced HIV infection (CD4 cell count < 50 × 106/l). The authors hypothesized that the severe disease temporally associated with institution of HAART was a consequence of availability of significant numbers of competent immune cells available to respond to a heavy, but previously subclinical, burden of latent mycobacterial infection.

HIV infection has been shown to dysregulate immune function within 7 days of in vitro infection of human macrophage hybridoma cell lines and primary monocytes, with loss of IL-12, in addition to other cytokine dysregulatory actions [15]. IL-12 is considered to be important for host cell defences in human and animal models of infection with M. avium complex [16] and C. neoformans [17]. Protease inhibitors such as indinavir have been shown to partially correct the cytokine dysregulation exhibited by HIV-infected patients within 2 weeks of starting therapy [18] (although measurement of IL-12 levels were not reported here).

Our findings are consistent with the hypothesis that combination antiretroviral therapy enhanced immune function and unmasked latent infection in two patients and precipitated clinically apparent meningitis in a third patient in response to residual cryptococcal antigen. We predict that patients with advanced HIV disease characterized by low CD4 cell counts or high HIV viral loads are the individuals most at risk of having a sufficient burden of latent opportunistic pathogens to stimulate a pro-inflammatory immune response following relative immune restitution produced by HAART.

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Keywords:

Cellular immunity; opportunistic infections; antiviral therapy

© 1998 Lippincott Williams & Wilkins, Inc.