T-Cell Deficiency in Dual Infection With Cytomegalovirus and Pneumocystis jiroveci Pneumonia

Introduction

Pneumocystis jiroveci pneumonia (PJP) is uncommon in persons with normal cell-mediated immunity. Conditions that predispose to PJP include primary cellular immunodeficiency, malignancy, immunosuppressive treatment, prematurity, malnutrition, and some viral infections.1–4 While the primary risk factor for PJP in the infant presented here appears to be immunosuppression due to cytomegalovirus (CMV) infection, steroids used to treat both the initial respiratory distress and the PJP likely contributed significantly to the outcome. This report discusses the complicated relationship between CMV and steroids in inducing lymphopenia and PJP, as well as other factors that may have contributed to the infant’s outcome.

Case Report

A male infant was born at 36 weeks gestation by caesarean section to a 16-year-old mother who denied prenatal infection, alcohol, tobacco, and illicit drug use. Apgar scores were 8 at 1 min and 9 at 5 min. Birth weight, length, and head circumference were at 25th, 50th, and 50th percentiles for corrected age. At 4 days of age, he required phototherapy for jaundice (Table 1), which resolved before discharge. Toxoplasmosis, rubella, CMV, and herpes simplex IgM (TORCH) titers were negative. Because of wide anterior fontanel, at 7 weeks of age he underwent neurologic evaluation and CT of the brain; both were normal. The infant received his first set of immunization (DTaP, Hib) and second hepatitis immunization at 6 weeks of age.

At 10 weeks of age, the infant developed fever (100.3°F axillary), fussiness, and decreased oral intake. On admission by transfer from an outlying hospital 2 days later, respiratory rate was 70–80 per minute with intercostal and subcostal retractions; lungs were clear to auscultation with good air movement, and oxygen saturation was 100% on oxygen at 2 L/min via nasal cannula. He had jaundice, mild hepatomegaly, left dysconjugate gaze with ptosis, and hypotonia. Weight, height, and head circumference were 35th, 35th, and 30th percentiles for corrected age.

Initial CXR was notable for normal cardiothymic silhouette, diffuse right lung infiltrates with air bronchogram, and haziness over the left perihilar area. Hepatitis was present (Table 1). Negative/normal studies included influenza antigens, respiratory syncytial virus antigen, urinalysis, lumbar puncture, blood culture, thyroid function, and CT of the head. He was treated with ampicillin, cefotaxime, and dexamethasone 0.7 mg every 6 h, and also with furosemide and aldactone. Lymphopenia, not present on admission, developed by 10 days after hospitalization with absolute lymphocyte count of 2,300 k/µL, CD3 of 1,576, and CD4 of 535 (Table 1). Serum IgM anti-CMV titer was elevated at 200 mg/dL (normal titer 31–120 mg/dL). Other TORCH titers were negative. Urine culture was positive for CMV 3 days after admission. Human immunodeficiency virus by HIV (ultra quantitative) PCR was negative for infant and mother. Ophthalmologic exam was normal 4 days after admission.

On day 10 of hospitalization, respiratory failure developed that required mechanical ventilation. High-resolution chest CT showed diffuse bilateral interstitial infiltration. Bronchoalveolar lavage fluid was positive for CMV by culture within 3 days and for PJP by silver stain. Stains were negative for fungi and bacteria. Previous antibiotics were discontinued; steroids were increased to 1.4 mg dexamethasone for 1 day followed by dexamethasone 0.7 mg (2 mg/kg) every 6 h; ganciclovir at 5 mg/kg/dose twice per day and trimethoprim–sulfamethoxazole at 5 mg/kg/dose twice per day were begun. Immunoglobulins obtained after infusion of fresh-frozen plasma (as part of resuscitation but also consistent with CMV infection) were elevated with IgG 861 mg/dL, IgM 200 mg/dL, and IgA 43 mg/dL. After 1 week, the child was weaned from the ventilator. Dexamethasone was changed to prednisolone 3 mg, 3 times daily for a week and then weaned by 50% weekly to 1 mg twice daily on discharge at age 5 months and to zero 1 week later, with 11-week duration of systemic steroids.

Because of persistent lymphopenia (Table 1), mitogen studies were obtained. Response was decreased to phytohemagglutinin and concanavalin A, negative to tetanus, but normal to pokeweed mitogen and Candida (Table 2).

Pneumonitis cleared slowly. Brain CT and MRI demonstrated calcifications consistent with significant brain involvement with CMV. Sensorineural hearing loss was confirmed by brain auditory evoked response. Excessive slowing of the left parietal leads on EEG suggested left parietal occipital cortical dysfunction consistent with encephalopathy. EEG 1 month later was unchanged.

Predigested formula per continuous nasogastric feed at >160 cal/kg was required for marginal weight gain. Developmental status improved minimally. A month after discharge clinical condition was unchanged. He was transferred to home (2 h away) with hospice support. The infant died unattended in his crib at 10 months of age. Autopsy was not performed.

Discussion

In the infant under 3 weeks of age with CMV presenting with central nervous system symptoms, hepatitis, retinitis, or pneumonia, the diagnosis is congenital CMV. Perinatal CMV may present as pneumonitis (most commonly), hepatitis, lymphadenopathy, neurologic sequelae, or sepsis-like syndrome, usually at 2–3 months of age. Because our patient had negative IgM TORCH titers at birth, because he had a normal neurologic exam at 7 weeks of age, because brain CT was normal at 7 weeks of age and on admission, and because he became ill at 10 weeks of age, he had perinatal CMV.

CMV and other herpesviruses may induce transient or persistent immunodeficiency.1^,2 Tu noted persistent and selective CD4+ lymphopenia in immunocompetent young children with CMV, with decreased production of interferon gamma by those cells. Carney noted decreased CD4 T-cell numbers, with CD4/CD8 ratio reversal and decreased lymphocyte proliferative response to Con A during acute CMV infection; all immunologic abnormalities normalized during recovery.3 In 7 infants <2 years of age with congenital CMV, specific CMV CD4 responses were almost undetectable. Infected monocytes have a decreased ability to present antigens including Candida albicans to lymphocytes.1 In patients with HIV, those with active CMV disease had the lowest and those with no active CMV disease had the highest number of CD4 cells as well as a broader repertoire of CMV-specific CD8.4 In young children with acute CMV, the decrease in number and function of CMV-specific CD4+ cells is permissive for prolonged virus secretion.2 Most of 104 children with congenital CMV studied by Pass1 continued to excrete virus until age 5 years. Viruria ceased with re-establishment of the lymphocyte blastogenic response to CMV. Decreased CMV-specific cytotoxic T-cell activity and impaired NK cell-mediated clearance by the virus may also result.5^,6 In an infant with minimal acquired immunity, the destruction of HLA expression on the surface of infected cells prevents display of viral peptides for T-cell recognition. CMV also encodes a molecule that can bind to immunoglobulin-like transcript 2, which protects the infected cell from NK-mediated and CD8 cytotoxic T-cell-mediated destruction. CD4 T-cell activation may be reduced by the decrease in antigen presentation, as well as by CMV interference with class II MHC presentation.

Our infant with perinatal CMV demonstrated the same changes in lymphocyte subset numbers and function as in the above studies. At birth and at time of admission at 12 weeks of age (8 weeks corrected age), total lymphocyte numbers were normal despite the stress of severe respiratory disease. By a week later when he had respiratory failure, lymphocyte numbers were low, especially CD4+ cells. The very slow improvement in his condition despite treatment of CMV (gancyclovir for 3 weeks, 1 dose of IVIG before labs were returned) is consistent with the findings of Pass and others regarding the slow recovery from CMV in young children, as well as the higher mortality in patients with CMV who developed PJP, regardless of other underlying condition.

Sritippayawan’s7 reported case of dual infection in a malnourished toddler was notable for low NK cells, lymphopenia, and impaired response to phytohemagglutinin (PHA), with normalization of lymphocyte subsets with treatment of CMV, improved nutrition, and clinical recovery. (This child was not treated with steroids.) Similarly to other cases of congenital and perinatal CMV in infants, and to other very ill-infected children, our patient developed lymphopenia, especially CD4 lymphopenia, which improved slowly but did not normalize by 6 months of age. CD4 lymphopenia and decreased function are reflected in the diminished activation response to PHA and concanavalin A (Con A). Carney also noted selective decrease in CD4 lymphocytes and diminished lymphocyte responses to Con A during acute disease, with improvement in both CD4 numbers and function with recovery.3 In 1993, Timon8 reported impaired cellular immune response to Con A, PHA, and pokeweed mitogen (PWM) by peripheral blood mononuclear cells from children 3 months to 7 years of age with acute CMV infection. The normal response to PWM in our patient likely reflects activation of lymphocytes other than the CD4+ cells. Given the absence of any Candida infection, the normal response to Candida by in vitro stimulation may suggest that the cells responsive to Candida were different from those subverted by CMV. A study of patients with primary immune deficiency of all ages found that response to Con A was the most reliable mitogen/antigen in identifying patients with immunodeficiency.9

P. jiroveci was first identified as a pathogen in premature infants with interstitial pneumonia in Europe during and after World War II. Infection becomes clinically apparent in those with impaired cellular immunity. Low CD4+ lymphocyte count may indicate high risk for PJP in non-HIV immunosuppressed patients. Burke and Good reported a series of 31 children and 15 adults who developed PJP; almost all were immunodeficient or immunosuppressed.9 Stagno10 reported in 1981 that of 104 infants hospitalized with pneumonia between the ages of 1 and 3 months, 18% had PJP; CMV was isolated from 20%; two had concomitant CMV infection and PJP. Prematurity, male sex, and lower weight were more common in infants with mixed infections. Three of the 5 deaths occurred in infants with CMV infection. In a series of 18 patients Hui and Kwok identified these risk factors: HIV infection (33%); steroid immune suppression, usually with other immunosuppressive drugs (60%); and congenital CMV (5.6%). CMV appeared to be the immunosuppressive agent in 1 infant and 2 adults with both PJP and CMV pneumonitis.12 Mortality was 33% overall, 40% in patients with concomitant bacterial or viral pneumonia, and 43% in the group receiving steroids as adjunctive treatment. None of the HIV-infected patients died. PJP may also occur when malnutrition induces T-cell dysfunction and in otherwise apparently immunologically normal infants with lymphopenia.13^–15 Neonatal rats born vaginally acquire Pneumocystis at or very shortly after birth.16 Most of the studies utilizing animal models of PCP entail steroid immunosuppression for induction of disease.

Similarly to many of the reported cases (of CMV and) of Pneumocystis in children, our infant was an ex-premie, at high risk nutritionally on admission and with very slow weight gain despite gavage feeding of high-calorie formula.11^,17 In his discussion of the Pneumocystis epidemic in premature infants after World War II, Goldman17 notes that initially malnutrition with its adverse effect on development of T cells, especially CD4 T cells, may have contributed to the epidemic. Affected infants were much more likely to have received blood transfusions that were likely often CMV-positive. In addition to the immune suppression by CMV infection per se, the stress of the CMV pneumonia with respiratory distress could have contributed to the lymphopenia and subsequent susceptibility to PJP. The epidemic did not clear until blood transfusions in premature infants and the use of non-disposable needles and syringes were no longer in practice. The epidemic is postulated to be due to a retroviral cause, but we feel that CMV-induced immune suppression in these premature infants was likely a critical component in their development of PJP.

Because the inflammatory response to PJP correlates with alveolar damage and respiratory failure, standard of care includes treatment with systemic steroids as well as trimethoprim/sulfamethoxazole. However, systemic steroids may be the only immunosuppressive agent in a patient with PJP.10^,12 Mansharamani et al.19 noted that in otherwise healthy adult patients hospitalized with PJP pneumonia, 91% had a CD4+ count of <300 cells/µL, along with 39%–46% of patients receiving long-term corticosteroid in the unknown or low-risk groups. Host defense against PJP entails an initial innate immune response as well as adaptive responses involving alveolar macrophages, T cells, NK cells, and dendritic cells.19^,20 Alveolar macrophages decrease in steroid-treated and PJP-infected rats;21 removal of steroids rapidly and treatment of PJP slowly resulted in rebound in alveolar macrophages. Both innate and adaptive responses were likely compromised in our patient by prematurity, steroid treatment, and CMV infection. In Qureshi’s model, mice infected with CMV and PCP,22 CD4 T cells were decreased, CD 8 cells were increased in the lungs and lymph nodes, and there were reduced numbers of MHC-II cells in the lung and lymph nodes 7 days after infection (note that our patient “crashed” 10 days after admission). Dually infected mice lost more weight and had delayed clearance of PJP compared to mice without CMV, similar to the course of our patient. In a piglet model,23 the group treated with methylprednisolone weekly gained weight more slowly, had atrophy of the thymus and diffuse lymphopenia, and developed PCP pneumonia, whereas the untreated group remained healthy. Dexamethasone suppresses activation of macrophages, neutrophils, CD4+ and CD8+ T cells, and other adaptive immune responses; prednisolone inhibits the monocyte-dependent proliferative response required for cell-mediated immunity. Steroid treatment may result in decreased total T cells, an effect exacerbated by malnutrition, although macrophage migration inhibitory factor activity is spared.24 Glucocorticoids impair differentiation of and antigen presentation by dendritic cells.25 Use of systemic and topical steroids have also resulted in fulminant CMV infection.26^,27 In a murine model of Pneumocystis, infection resolved following withdrawal of corticosteroids.28

Corticosteroids activate CMV in vitro. In patients with HIV and PJP, patients who had CMV cultured from BAL fluid (as did our patient) had 2 times higher mortality within 3 months as those not treated with steroids. Differences in CD4 count did not affect outcome in these adult patients.29 Terblanche et al. recently reported a randomized controlled trial in infants up to 18 months of age with HIV exposure and with clinical PJP, adjunctive steroid treatment begun early may improve survival but did not decrease recovery time or oxygen requirement.29 Renal transplant patients who do not receive steroids have a lower incidence of CMV infection and also of Pneumocystis pneumonia.31

Lymphopenia has also been associated with poor outcome in acutely unwell infants as well as in patients with CMV infection after bone marrow transplant.32 Because the systemic steroids were begun on admission, and bronchoscopy was not performed nor was a second CBC with differential obtained until the infant required intubation 10 days later, we can only speculate as to onset time(s) of lymphopenia and of PJP. However, a review of the literature failed to identify infectious complications or lymphopenia due to steroids after 2 weeks or less of therapy in humans. Further, our patient’s lymphocyte count showed only partial recovery 2 months after steroids were discontinued.

Rowling13 and Sritippayawan7 each reported PCP in an infant with CMV with clinical recovery and resolution of initially low absolute lymphocyte count after treatment with gancyclovir and sulfamethoxazole. Failure of our patient to recover is likely multifactorial. As in Stagno’s series of infants hospitalized with pneumonia with poor outcome, our patient was premature, male, and had low weight.11 As in Hui and Kwok’s series,12 our patient had CMV as a major immunosuppressive factor, was an infant, was treated with steroids, and had a poor outcome. Pneumonia (due to CMV) and respiratory distress were severe enough at admission that the patient was treated with systemic steroids. Since the institution of systemic steroids was just 10 days prior to respiratory failure and lymphopenia was identified, and the steroids were discontinued 3 weeks prior to the penultimate visit, with minimal recovery of the lymphocyte count, it is likely that the CMV infection was most responsible for the persistent immunosuppression. Work of breathing resulted in borderline nutrition with high caloric needs. Although the usual course of therapy is 3 weeks, discontinuing gancyclovir after 3 weeks while the infant was still being treated with significant doses of steroids, and/or a qualitative pre-existing lymphocyte defect, may have also contributed to lack of recovery.

In conclusion, perinatal CMV may cause significant cellular immune suppression that is usually transient, but which has significant potential for opportunistic infection. In the absence of HIV infection, identification of PJP should trigger a search for viruses capable of suppressing the immune system as well as primary cellular immune deficiency. While the evaluation is in progress, the child should be treated as if a defect of cell-mediated immunity is present. If indicated, antiviral medication may be lifesaving. Nutrition should be optimized and steroids tapered as rapidly as possible.