Identification of dynamically distinct subpopulations of T lymphocytes that are differentially affected by HIV.

We examined the effects of human immunodeficiency virus infection on the turnover of CD4 and CD8 T lymphocytes in 17 HIV-infected patients by 30 min in vivo pulse labeling with bromodeoxyuridine (BrdU). The percentage of labeled CD4 and CD8 T lymphocytes was initially higher in lymph nodes than in blood. Labeled cells equilibrated between the two compartments within 24 h. Based on mathematical modeling of the dynamics of BrdU-labeled cells in the blood, we identified rapidly and slowly proliferating subpopulations of CD4 and CD8 T lymphocytes. The percentage, but not the decay rate, of labeled CD4 or CD8 cells in the rapidly proliferating pool correlated significantly with plasma HIV RNA levels for both CD4 (r = 0.77, P < 0.001) and CD8 (r = 0.81, P < 0.001) T cells. In six patients there was a geometric mean decrease of greater than 2 logs in HIV levels within 2 to 6 mo after the initiation of highly active antiretroviral therapy; this was associated with a significant decrease in the percentage (but not the decay rate) of labeled cells in the rapidly proliferating pool for both CD4 (P = 0.03) and CD8 (P < 0.001) T lymphocytes. Neither plasma viral levels nor therapy had an effect on the decay rate constants or the percentage of labeled cells in the slowly proliferating pool. Monocyte production was inversely related to viral load (r = -0.56, P = 0.003) and increased with therapy (P = 0.01). These findings demonstrate that HIV does not impair CD4 T cell production but does increase CD4 and CD8 lymphocyte proliferation and death by inducing entry into a rapidly proliferating subpopulation of cells.

Guidelines for the safe administration of high-dose interleukin-2.

High-dose interleukin-2 (IL-2) results in objective clinical regression of metastatic cancer in 15% to 17% of patients with melanoma and renal cell carcinoma. Durable complete regression of all metastases is seen in 6% to 8% of patients. Based on these findings, the U.S. Food and Drug Administration has approved the use of high-dose IL-2 for the treatment of patients with metastatic melanoma and renal cell carcinoma. Interleukin-2 administration is associated with many different side effects, and after many years of use, clinicians have learned how to safely administer high-dose IL-2. This article details practical guidelines for the safe administration of high-dose IL-2.

Adoptive transfer of cloned melanoma-reactive T lymphocytes for the treatment of patients with metastatic melanoma.

This report describes a phase I study of the adoptive transfer of cloned melanoma antigen-specific T lymphocytes for therapy of patients with advanced melanoma. Clones were derived from peripheral blood lymphocytes or tumor-infiltrating lymphocytes of patients who had received prior immunization with the melanoma-associated antigen, gpl00. In response to its cognate antigen, each clone used for treatment secreted large amounts of interferon-gamma and granulocyte-macrophage colony-stimulating factor, lesser amounts of interleukin (IL)-2 and tumor necrosis factor-alpha, and little or no IL-4 and IL-10. Clones also demonstrated recognition of human leukocyte antigen-matched melanomas using cytokine secretion and lysis assays. Twelve patients received 2 cycles of cells alone; 11 patients received additional cycles of cells and were randomized between two schedules of IL-2 (125,000 IU/kg subcutaneously daily for 12 days versus 720,000 IU/kg intravenously every 8 h for 4 days). A total of 51 cycles of cells were administered, with an average of 1 x 10(10) cells per cycle. Peripheral blood samples were analyzed for persistence of transferred cells by T-cell receptor-specific polymerase chain reaction. Transferred cells reached a maximum level at 1 h after transfer but rapidly declined to undetectable levels by 2 weeks. One minor response and one mixed response were observed (both in the high-dose IL-2 arm). This report demonstrates the safety and feasibility of cloned T-cell transfer as a therapy for patients with cancer. The lack of clinical effectiveness of this protocol suggests that transfer of different or additional cell types or that modulation of the recipient host environment is required for successful therapy.

Clinical pathways for managing patients receiving interleukin 2.

As biologic therapies enter the mainstream for cancer and HIV treatments, clinicians need the knowledge and expertise to safely and competently care for their patients who are undergoing these therapies. This article provides an overview of the immune system, emphasizing the elements that are affected by the biologic agent interleukin 2 (lL-2), lL-2 has been approved for use in the treatment of metastatic renal cell carcinoma and metastatic melanoma. Clinical trials currently are being conducted to determine its use in treating other cancers. The severity of side effects of lL-2 varies with the dose, route, and schedule of administration. The most common effects with all methods of administration are flu-like symptoms. Because the side effects of lL-2 are relatively predictable, clinical pathways offer practical tools for anticipating and managing the toxicities associated with lL-2 administration.

Decreased tolerance to interleukin-2 with repeated courses of therapy in patients with metastatic melanoma or renal cell cancer.

High-dose interleukin-2 (IL-2) therapy has a response rate of approximately 20% in patients with metastatic melanoma and renal cell cancer. Animal models have shown that the anti-tumor effects of IL-2 are dose and schedule dependent, and one report has shown that patients with melanoma who responded to IL-2 therapy received more doses of IL-2 than did those who did not respond. The current study evaluated patients' tolerance to IL-2 over multiple courses of therapy and the factors that affected the number of doses delivered. Patients with metastatic melanoma or renal cell cancer who received at least two consecutive courses of high-dose intravenous IL-2 alone from October 1, 1985 through December 31, 1996 were evaluated. Patients served as their own controls in paired analyses. The number of doses tolerated from one course to the next and the reasons for stopping therapy were analyzed. One hundred fifty-nine patients received two or more courses of therapy during the study. The median number of doses of high-dose IL-2 decreased from course 1 (15 doses) to course 2 (12 doses) (p2 = 0.0001). Pretreatment factors were not found to significantly influence the decrease in the number of doses delivered. Only 2 of 33 separate toxic effects resulting in discontinuation of IL-2 dosing were found to be significantly different between courses. After adjusting for multiple tests of statistical significance, serum aspartate aminotransferase elevations were more likely to stop course 1 (p2 = 0.0033) and creatinine elevations were more likely to stop course 2 (p2 = 0.00007). The influence of renal toxicity was further assessed by comparing the median creatinine value at the time IL-2 dosing was discontinued. This difference was found to be significant when cycle 1 of course 1 (1.5 mg/dL) was compared with cycle 1 of course 2 (1.8 mg/dL; p2 = 0.0001). When pretreatment factors were analyzed, male sex (p2 = 0.006), a diagnosis of renal cell cancer (p2 = 0.008), previous nephrectomy (p2 = 0.001), and older age (p2 = 0.0055) were significantly associated with the development of renal toxicity that resulted in discontinuation of IL-2 therapy. Furthermore, the same four patient subsets had higher baseline creatinine values in individual univariate analyses. This study identified subsets of patients who tolerated less IL-2 with repeated courses. The decreasing tolerance to IL-2 was associated primarily with elevations in creatinine. Finding ways to ameliorate the renal toxicity seen during IL-2 therapy in this patient population may allow an increase in the number of IL-2 doses administered and potentially an increase in clinical response.

Lymph node architecture preceding and following 6 months of potent antiviral therapy: follicular hyperplasia persists in parallel with p24 antigen restoration after involution and CD4 cell depletion in an AIDS patient.

OBJECTIVES: To evaluate changes in architecture, viral RNA, and viral protein over 6 months in lymph nodes from retroviral-naïve HIV-infected persons before and after commencing highly active antiretroviral therapy (HAART). METHODS: Nine antiretroviral-naïve HIV-infected persons had lymph nodes excised at baseline and at 2 and 6-8 months after beginning a four-drug combination regimen containing zidovudine, lamivudine, nevirapine, and indinavir. Two patients had AIDS. Lymph nodes were examined by immunohistochemical staining for Gag p24 HIV, CD3, CD21, CD20, HAM 56, and Ki67 antigens and by in-situ hybridization (ISH) for HIV RNA and H3-histone RNA. RESULTS: Eight of nine baseline lymph nodes showed follicular hyperplasia and germinal center and paracortical mononuclear cell activation. At 2 months, the lymph nodes from seven patients, including the AIDS patients, showed more follicular hyperplasia and activation than their baseline specimens but with decreased mononuclear cell activation. By 6 months, seven lymph nodes were less hyperplastic and activated than their corresponding 2 month specimens. Combined ISH/immunohistochemical staining of baseline lymph nodes revealed productively infected T (CD3) and B (CD20) cells and macrophages (HAM56+). HIV RNA-positive mononuclear cells were infrequent at 2 months, and rare at 6 months. HIV RNA was still associated with follicular dendritic cells (FDC) at 2 months, but not at 6 months. HIV p24-positive antigen in germinal centers persisted through all 6, and the one 8 month specimens. The baseline lymph nodes from one of the AIDS patients was involuted and T cell depleted, whereas the follow-up lymph nodes were hyperplastic with normal T cell levels. CONCLUSION: Follicular hyperplasia and cell activation, possibly caused by persistent viral protein in germinal centers, may help explain why HIV viremia rebounds so rapidly after the interruption of HAART. Restoration of architecture may follow the treatment of patients with AIDS who initially had involuted and CD4 cell-depleted lymph nodes.

Brain metastasis after immunotherapy in patients with metastatic melanoma or renal cell cancer: is craniotomy indicated?

The purpose of this study was to evaluate the outcome of surgical treatment of brain metastasis in patients with metastatic melanoma or renal cell cancer after interleukin-2 (IL-2) therapy. A retrospective analysis was conducted at the Surgery Branch, National Cancer Institute. All patients with a diagnosis of metastatic melanoma or renal cell cancer who received IL-2 from January 1, 1985 to January 1, 1996 (n = 1385) were screened for the development of brain metastasis. Forty patients underwent surgical treatment of brain metastasis that developed after initiating IL-2 therapy. Thirty-six were rendered free of disease after resection of a single metastasis and were the focus of this study. Twenty-two of the 36 patients achieved a clinical response (10 complete responses and 12 partial responses) at extracranial sites of disease after IL-2-based immunotherapy and before the development of brain metastasis. The median disease-free interval in the brain after resection of a single metastasis was 21, 7, and 3 months for patients achieving a complete response, partial response, and no response (CR, PR, and NR) to IL-2 therapy, respectively. The median survival after craniotomy for these three groups of patients was 23, 17, and 7 months, respectively. The disease-free interval in the brain and the overall survival after craniotomy were significantly longer for patients achieving a CR to previous immunotherapy when compared with patients achieving a PR or NR. Of the 10 patients who had achieved a prior CR, 8 remained disease free in the brain at last follow-up, 6 remained alive beyond 1 year, and 3 > 4 years. Twenty-five patients experienced neurologic symptoms before craniotomy and all had complete resolution of their symptoms after surgery. Surgical treatment of single brain metastasis in patients with metastatic melanoma or renal cell cancer is indicated in carefully selected patients. The benefits of resection include palliation of symptoms and the potential for a prolonged disease-free interval in the brain.

Impact of cytokine administration on the generation of antitumor reactivity in patients with metastatic melanoma receiving a peptide vaccine.

Patients with metastatic melanoma were immunized with an immunodominant peptide derived from the gp100 melanoma-melanocyte differentiation Ag that was modified to increase binding to HLA-A+0201. A total of 10 of 11 patients who received the g209-2M peptide alone developed precursors reactive with the native g209 peptide, compared with only 5 of 16 patients who received g209-2M peptide plus IL-2 (p2 = 0.005). Peptide reactivity closely correlated with the recognition of HLA-A+0201 melanoma cells (p < 0. 001). The decrease in immune reactivity when peptide was administered with IL-2 appeared specific for the immunizing peptide, since reactivity to an influenza peptide resulting from prior exposure was not affected. Preexisting antitumor precursors did not decrease when peptide plus IL-2 was administered. The administration of GM-CSF or IL-12 also resulted in a decrease in circulating precursors compared with the administration of peptide alone, though not as great a decrease as that seen with IL-2. Immunization with peptide plus IL-2 did, however, appear to have clinical impact since 6 of the 16 patients (38%) that received peptide plus IL-2 had objective cancer regressions. It thus appeared possible that immunization with peptide plus IL-2 resulted in sequestering or apoptotic destruction of newly activated immune cells at the tumor site. These represent the first detailed studies of the impact of immunization with tumor peptides in conjunction with a variety of cytokines in patients with metastatic cancer.

Prospective randomized trial of the treatment of patients with metastatic melanoma using chemotherapy with cisplatin, dacarbazine, and tamoxifen alone or in combination with interleukin-2 and interferon alfa-2b.

PURPOSE: The combination of chemotherapy with immunotherapeutic agents such as interleukin-2 and interferon alfa-2b has been reported to provide improved treatment results in patients with metastatic melanoma, compared with the use of chemotherapy alone. We have performed a prospective randomized trial in patients with metastatic melanoma, comparing treatment with chemotherapy to treatment with chemoimmunotherapy. PATIENTS AND METHODS: One hundred two patients with metastatic melanoma were prospectively randomized to receive chemotherapy composed of tamoxifen, cisplatin, and dacarbazine or this same chemotherapy followed by interferon alfa-2b and interleukin-2. Objective responses, survival, and toxicity in the two groups were evaluated at a median potential follow-up of 42 months. RESULTS: In 52 patients randomized to receive chemotherapy, there were 14 objective responses (27%), including four complete responses. In 50 patients randomized to receive chemoimmunotherapy, there were 22 objective responses (44%) (P2 = .071), including three complete responses. In both treatment groups, the duration of partial responses was often short, and there was a trend toward a survival advantage for patients receiving chemotherapy alone (P2 = .052; median survival of 15.8 months compared with 10.7 months). Treatment-related toxicities were greater in patients receiving chemoimmunotherapy. CONCLUSION: With the treatment regimens used in this study, the addition of immunotherapy to combination chemotherapy increased toxicity but did not increase survival. The use of combination chemoimmunotherapy regimens is not recommended in the absence of well-designed, prospective, randomized protocols showing the benefit of this treatment strategy.

MHC class I-restricted recognition of a melanoma antigen by a human CD4+ tumor infiltrating lymphocyte.

It is generally considered that MHC class I-restricted antigens are recognized by CD8+ T cells, whereas MHC class II-restricted antigens are recognized by CD4+ T cells. In the present study, we report an MHC class I-restricted CD4+ T cell isolated from the tumor infiltrating lymphocytes (TILs) of a patient with metastatic melanoma. TIL 1383 I recognized HLA-A2+ melanoma cell lines but not autologous transformed B cells or fibroblasts. The antigen recognized by TIL 1383 I was tyrosinase, and the epitope was the 368-376 peptide. Antibody blocking assays confirmed that TIL 1383 I was MHC class I restricted, and the CD4 and CD8 coreceptors did not contribute significantly to antigen recognition. TIL 1383 I was weakly cytolytic and secreted cytokines in a pattern consistent with it being a Th1 cell. The avidity of TIL 1383 I for peptide pulsed targets is 10-100-fold lower than most melanoma-reactive CD8+ T cell clones. These CD4+ T cells may represent a relatively rare population of T cells that express a T-cell receptor capable of cross-reacting with an MHC class I/peptide complex with sufficient affinity to allow triggering in the absence of the CD4 coreceptor.

Immunizing patients with metastatic melanoma using recombinant adenoviruses encoding MART-1 or gp100 melanoma antigens.

BACKGROUND: The characterization of the genes encoding melanoma-associated antigens MART-1 or gp100, recognized by T cells, has opened new possibilities for the development of immunization strategies for patients with metastatic melanoma. With the use of recombinant adenoviruses expressing either MART-1 or gp100 to immunize patients with metastatic melanoma, we evaluated the safety, immunologic, and potential therapeutic aspects of these immunizations. METHODS: In phase I studies, 54 patients received escalating doses (between 10(7) and 10(11) plaque-forming units) of recombinant adenovirus encoding either MART-1 or gp100 melanoma antigen administered either alone or followed by the administration of interleukin 2 (IL-2). The immunologic impact of these immunizations on the development of cellular and antibody reactivity was assayed. RESULTS: Recombinant adenoviruses expressing MART-1 or gp100 were safely administered. One of 16 patients with metastatic melanoma receiving the recombinant adenovirus MART-1 alone experienced a complete response. Other patients achieved objective responses, but they had received IL-2 along with an adenovirus, and their responses could be attributed to the cytokine. Immunologic assays showed no consistent immunization to the MART-1 or gp100 transgenes expressed by the recombinant adenoviruses. High levels of neutralizing antibody were found in the pretreatment sera of the patients. CONCLUSIONS: High doses of recombinant adenoviruses could be safely administered to cancer patients. High levels of neutralizing antibody present in patients' sera prior to treatment may have impaired the ability of these viruses to immunize patients against melanoma antigens.

A breast and melanoma-shared tumor antigen: T cell responses to antigenic peptides translated from different open reading frames.

Infusion of TIL586 along with IL-2 into the autologous patient with metastatic melanoma resulted in the objective regression of tumor. Here, we report that screening a cDNA library from the 586mel cell line using CTL clones derived from TIL586 resulted in the isolation of a gene, CAG-3 (cancer Ag gene 3). Sequence analysis revealed that CAG-3 encodes an open reading frame identical to NY-ESO-1, which was recently reported to be recognized by autologous serum from a patient with esophageal cancer. Thus, NY-ESO-1 appears to be an immune target for both Ab- and T cell-mediated responses. Significantly, NY-ESO-1-specific CTL clones were capable of recognizing two HLA-A31-positive fresh and cultured breast tumors. To our knowledge, this represents the first direct demonstration that tumor-specific CTL clones can recognize both breast and melanoma tumor cells. A 10-mer antigenic peptide ESO10-53 (ASGPGGGAPR) was identified from the normal open reading frame of NY-ESO-1 based on its ability to sensitize HLA-A31-positive target cells for cytokine release and specific lysis. Interestingly, two additional CTL clones that were sensitized with NY-ESO-1 recognized two overlapping antigenic peptides derived from an alternative open reading frame of the same gene. These findings indicate that CTLs simultaneously responded to two different gene products translated from the normal and alternative reading frames of the same gene. Understanding of this mechanism by which the alternative reading frame is translated may have important implications in tumor immunology.

Splenectomy in a child with chronic Mycobacterium avium complex infection and splenic sequestration.

Mycobacterium avium complex infections (MAC) are being reported with increasing frequency in immunocompromised patients. When these infections become resistant to standard antibiotic therapy, treatment with interferon-gamma (IFN-gamma) can be helpful. Pain, fever, splenic enlargement, and cytopenias caused by splenic sequestration developed during IFN-gamma treatment in a 9-year-old boy and were successfully treated by splenectomy. The development of IFN-gamma-induced splenic sequestration and cytopenias in MAC-infected patients represents a new indication for splenectomy.

Immunologic and therapeutic evaluation of a synthetic peptide vaccine for the treatment of patients with metastatic melanoma.

The cloning of the genes encoding cancer antigens has opened new possibilities for the treatment of patients with cancer. In this study, immunodominant peptides from the gp100 melanoma-associated antigen were identified, and a synthetic peptide, designed to increase binding to HLA-A2 molecules, was used as a cancer vaccine to treat patients with metastatic melanoma. On the basis of immunologic assays, 91% of patients could be successfully immunized with this synthetic peptide, and 13 of 31 patients (42%) receiving the peptide vaccine plus IL-2 had objective cancer responses, and four additional patients had mixed or minor responses. Synthetic peptide vaccines based on the genes encoding cancer antigens hold promise for the development of novel cancer immunotherapies.

Heterozygosity for a defective gene for CC chemokine receptor 5 is not the sole determinant for the immunologic and virologic phenotype of HIV-infected long-term nonprogressors.

HIV-1-infected long-term nonprogressors are a heterogeneous group of individuals with regard to immunologic and virologic markers of HIV-1 disease. CC chemokine receptor 5 (CCR5) has recently been identified as an important coreceptor for HIV-1 entry into CD4+ T cells. A mutant allele of CCR5 confers a high degree of resistance to HIV-1 infection in homozygous individuals and partial protection against HIV disease progression in heterozygotes. The frequency of CCR5 heterozygotes is increased among HIV-1- infected long-term nonprogressors compared with progressors; however, the host defense mechanisms responsible for nonprogression in CCR5 heterozygotes are unknown. We hypothesized that nonprogressors who were heterozygous for the mutant CCR5 gene might define a subgroup of nonprogressors with higher CD4+ T cell counts and lower viral load compared with CCR5 wild-type nonprogressors. However, in a cohort of 33 HIV-1-infected long-term nonprogressors, those who were heterozygous for the mutant CCR5 gene were indistinguishable from CCR5 wild-type nonprogressors with regard to all measured immunologic and virologic parameters. Although epidemiologic data support a role for the mutant CCR5 allele in the determination of the state of long-term nonprogression in some HIV-1- infected individuals, it is not the only determinant. Furthermore, long-term nonprogressors with the wild-type CCR5 genotype are indistinguishable from heterozygotes from an immunologic and virologic standpoint.

Tumor-infiltrating lymphocytes from human ovarian cancer patients recognize autologous tumor in an MHC class II-restricted fashion.

PURPOSE: To search for tumor-specific in vitro reactivity by lymphocytes derived from patients with ovarian carcinoma. METHODS: Tumor-infiltrating lymphocytes (TIL) were derived from primary or metastatic solid tumors and tumor-associated lymphocytes (TAL) were derived from ascites from 13 patients with ovarian cancer. TIL or TAL were cultured for approximately 30 to 60 days and studied for phenotype, cytotoxicity, and cytokine secretion in response to autologous tumor stimulation. RESULTS: Twenty-nine bulk TIL or TAL cultures were successfully established from 10 patients using various culture conditions. Thirteen cultures were predominantly CD4+ and 16 were mainly CD8+. In contrast to reports by others, none of the cultures tested were specifically lyric for autologous tumor. Five predominantly CD4+ bulk TIL (from four patients) preferentially secreted tumor necrosis factor-alpha and granulocyte macrophage-colony stimulating factor when stimulated with autologous tumor and not when stimulated by autologous Epstein Barr virus-B cells, fibroblasts, peripheral blood mononuclear cells, or allogeneic HLA matched or mismatched stimulators. This cytokine secretion was found to be MHC class-II restricted in three patients because it was inhibited by the anti-MHC class-II antibody IVA12 and the HLA-DR specific antibody L243. CONCLUSION: We believe these data are the first to suggest that tumor reactive CD4+ lymphocytes exist in some ovarian cancer patients. This finding may be useful in the development of novel immunotherapies for these patients.

Comparison of virus burden in blood and sequential lymph node biopsy specimens from children infected with human immunodeficiency virus.

BACKGROUND: Lymph nodes serve as reservoirs for the replication of human immunodeficiency virus (HIV) type 1. Comparison of serial measurements of virus burden in lymph nodes and peripheral blood after a change in antiretroviral therapy may provide insights into pathogenic mechanisms and permit a more accurate assessment of a therapeutic response. STUDY DESIGN: Nevirapine was added to the drug regiment of eight children with HIV infection treated with the combination of zidovudine and didanosine who had increasing levels of serum p24 antigen. Lymph node biopsies were performed at entry and after 12 weeks of therapy. RESULTS: Neither CD4 counts nor p24 antigen level correlated with the degree of viremia as measured by ribonucleic acid copy numbers in plasma. Correlations were found between HIV DNA copy number in peripheral blood mononuclear cells and HIV DNA copy number in lymph nodes (p = 0.02), as well as between peripheral blood CD4 counts and lymph node architecture. The HIV signals in the lymph nodes conformed to the anatomic organization of apical light zones in the germinal centers; however, in more advanced disease stages, organized germinal centers disappeared as evidence by a decline in the extent of the follicular dendritic network. CONCLUSIONS: Lymph node biopsies in this small number of HIV-infected children revealed a progressive loss of an organized architecture, especially of the follicular dendritic network. This correlated with a progressive loss of CD4+ cells but not with other measures of disease stage, including viral load, as measured by ribonucleic acid copy numbers.

Dynamics of virus versus host interaction in children with human immunodeficiency virus type 1 infection.

To investigate the dynamic interplay between human immunodeficiency virus type I (HIV-1) replication and the extent of immune destruction in HIV-1-infected children, virus burden in lymphoid tissues (LN) and peripheral blood was compared with changes in LN architecture and cytokine levels constitutively expressed in LN. In agreement with results of a preliminary study, the plasma HIV-1 RNA level correlated with the amount of provirus in LN. However, the level was also associated with a degree of destruction of lymphoid follicular architecture and an alteration of immune cytokine expression. Expression of interleukin (IL)-4 was higher in LN with higher virus replication. Reduction of plasma viremia was associated with an increase in IL-2 mRNA levels in LN. These findings suggest that measurable virus burden in the peripheral blood is not a simple reflection of viral replication in LN but is also influenced by the extent of progressive immune destruction.

Effect of immunization with a common recall antigen on viral expression in patients infected with human immunodeficiency virus type 1.

BACKGROUND: Activation of the immune system is a normal response to antigenic stimulation, and such activation enhances the replication of human immunodeficiency virus type 1 (HIV-1). We studied the effect of immunization with a common recall antigen on viral expression in HIV-1-infected patients, on the ability to isolate virus, and on the susceptibility to HIV-1 infection of peripheral-blood mononuclear cells (PBMCs) from control subjects not infected with HIV-1. METHODS: Thirteen HIV-1-infected patients and 10 uninfected adults were given a 0.5-ml booster dose of tetanus toxoid. Studies were performed to evaluate changes in the degree of plasma viremia, proviral burden, the ability to isolate HIV-1, and the susceptibility of PBMCs to acute infection in vitro. Two patients underwent sequential lymph-node biopsies for the assessment of viral burden in these tissues. RESULTS: All 13 HIV-1-infected patients had transient increase in plasma viremia after immunization, and the proviral burden increased in 11. These changes did not correlate with the base-line CD4+ T-cell counts. The lymph-node tissue also had increases in the proviral burden and viral RNA after immunization. The virus was more easily isolated from PBMCs from nine of the patients after immunization than before immunization. Despite considerable variability in the results, PBMCs from 7 of the 10 normal subjects were more easily infected in vitro with HIV-1 after immunization than before immunization. CONCLUSIONS: Activation of the immune system by an ongoing antigen-specific immune response to an exogenous stimulus transiently increases the expression of HIV-1 and may enhance the susceptibility of uninfected subjects to HIV-1.