Effect of recombinant human interleukin-6 (rhIL-6) and rhIL-3 on hematopoietic regeneration as demonstrated in a nonhuman primate chemotherapy model

Using a recently developed hepsulfam-induced pancytopenia model in rhesus macaques, we have studied the effects of recombinant human interleukin-6 (rhIL-6) and rhIL-3 on marrow regeneration. Control animals were given hepsulfam (1.5 g/m2 by a single 30-minute intravenous [i.v.] injection, n = 4), while study animals received hepsulfam followed by rhIL-6, rhIL-3, or a combination of rhIL-6 and rhIL-3 (n = 3 per study group). Each cytokine was administered by once- daily subcutaneous (SC) injection (15 micrograms/kg/d) for 3 weeks beginning the day after chemotherapy (days 2 through 22). Mean platelet counts in control animals were < 100,000/microL on days 15 through 24, with 50% of the counts < 50,000/microL and two of four animals requiring platelet transfusion. In the rhIL-6- and rhIL-6/rhIL-3- treated groups, the nadir mean platelet counts were 164,000 +/- 58,700/microL and 162,300 +/- 23,800/microL, respectively, and occurred on day 15. Platelet counts in the rhIL-3-treated group were similar to those in controls. Mean absolute neutrophil counts (ANCs) < 1,000/microL occurred on days 10 through 29 in control animals, days 8 through 15 in rhIL-6-treated animals, and days 6 through 8 and 13 in rhIL-6/rhIL-3-treated animals. The frequency of ANCs < 500/microL was significantly less in the rhIL-6- and rhIL-6/rhIL-3-treated groups versus control groups (2.7 +/- 0.6 and 2.0 +/- 1.0 vs 7.0 +/- 1.4 occurrences, respectively; P < .05). rhIL-3-treated animals had ANCs similar to those in controls; one animal died with septicemia on day 21. Monkeys receiving rhIL-6 were significantly more anemic during the cytokine administration period; however, the anemia resolved by day 24. Coadministration of rhIL-3 and rhIL-6 partially corrected the anemia. The data indicate that rhIL-6 prevents significant thrombocytopenia and shortens the neutropenic period in this chemotherapy model.     

Targeting CD137 enhances the efficacy of cetuximab

Treatment with cetuximab, an EGFR-targeting IgG1 mAb, results in beneficial, yet limited, clinical improvement for patients with head and neck (HN) cancer as well as colorectal cancer (CRC) patients with WT KRAS tumors. Antibody-dependent cell-mediated cytotoxicity (ADCC) by NK cells contributes to the efficacy of cetuximab. The costimulatory molecule CD137 (4-1BB) is expressed following NK and memory T cell activation. We found that isolated human NK cells substantially increased expression of CD137 when exposed to cetuximab-coated, EGFR-expressing HN and CRC cell lines. Furthermore, activation of CD137 with an agonistic mAb enhanced NK cell degranulation and cytotoxicity. In multiple murine xenograft models, including EGFR-expressing cancer cells, HN cells, and KRAS-WT and KRAS-mutant CRC, combined cetuximab and anti-CD137 mAb administration was synergistic and led to complete tumor resolution and prolonged survival, which was dependent on the presence of NK cells. In patients receiving cetuximab, the level of CD137 on circulating and intratumoral NK cells was dependent on postcetuximab time and host FcyRIIIa polymorphism. Interestingly, the increase in CD137-expressing NK cells directly correlated to an increase in EGFR-specific CD8⁺ T cells. These results support development of a sequential antibody approach against EGFR-expressing malignancies that first targets the tumor and then the host immune system.     

From the Cover: PNAS Plus: Comprehensive analysis of dengue virus-specific responses supports an HLA-linked protective role for CD8+ T cells

The role of CD8⁺ T cells in dengue virus infection and subsequent disease manifestations is not fully understood. According to the original antigenic sin theory, skewing of T-cell responses induced by primary infection with one serotype causes less effective response upon secondary infection with a different serotype, predisposing individuals to severe disease. A comprehensive analysis of CD8⁺ responses in the general population from the Sri Lankan hyperendemic area, involving the measurement of ex vivo IFNγ responses associated with more than 400 epitopes, challenges the original antigenic sin theory. Although skewing of responses toward primary infecting viruses was detected, this was not associated with impairment of responses either qualitatively or quantitatively. Furthermore, we demonstrate higher magnitude and more polyfunctional responses for HLA alleles associated with decreased susceptibility to severe disease, suggesting that a vigorous response by multifunctional CD8⁺ T cells is associated with protection from dengue virus disease.Dengue virus (DENV) is the etiologic agent of dengue fever (DF), the most significant mosquito-borne viral disease in humans. Disease can be caused by any of the four DENV serotypes (DENV1 to -4), which share 67–75% sequence homology with one another (1). DENV transmission occurs in more than 100 countries and is an increasing public health problem in tropical and subtropical regions (2). Demographic changes, urbanization, and international travel contribute to the expansion of geographical areas where transmission occurs, and all four DENV serotypes are now circulating in Asia, Africa, and the Americas (3, 4). Up to 100 million DENV infections occur every year (5), and severity can range from asymptomatic to an acute self-limiting febrile illness (DF). In a small proportion of patients, the disease can exacerbate and progress to dengue hemorrhagic fever (DHF) and/or dengue shock syndrome (DSS), characterized by severe vascular leakage, thrombocytopenia, and hemorrhagic manifestations (4).Although natural infection by any of the four DENV serotypes (primary infection) produces a lasting protective immunity against reinfection by the same serotype, it does not protect against infections with other serotypes (secondary infections) (6, 7). Epidemiologic studies have shown that the majority of individuals that develop DHF/DSS had been previously infected with a different serotype (8). Consequently, the development of DENV vaccines has been hampered by the potential risk of vaccine-related adverse events and the requirement to induce long-lasting protective immune responses against all four DENV serotypes simultaneously (9). The cause for the increased frequency of DHF following secondary infections has not been fully elucidated. One hypothesis is that serotype cross-reactive antibodies exacerbate disease by increasing infection of cells bearing Fcγ receptors, resulting in higher viral loads and more severe disease via this antibody-dependent enhancement (ADE) of infection (10, 11). Indeed, nonhuman primate and murine models have demonstrated that antibodies can lead to enhancement of DENV infection and disease in vivo (12–15).Another hypothesis postulates that T cells raised against the first infecting serotype dominate during a secondary heterologous infection in a phenomenon termed “original antigenic sin” (16, 17). This term was first applied to the humoral response to influenza epidemics (18) but has also been observed in CD8⁺ T-cell responses against lymphocytic choriomeningitis virus (19). This hypothesis postulates that, during secondary infection, expansion of preexisting lower avidity cross-reactive memory T cells dominate the responses over that of naïve T cells that are of higher avidity for the new DENV serotype. This expansion of low avidity T cells results in less efficient elimination of DENV-infected cells.A role for T cells in control of DENV infection is suggested by several studies that implicate HLA associations as a genetic component to variable susceptibility to DENV disease (20–26). However, it has not been addressed whether these associations might indicate a positive or detrimental role for T-cell responses. One major obstacle to the elucidation of the function of T cells is the lack of a comprehensive characterization of HLA-restricted DENV responses in the context of natural infection.Herein, we present a comprehensive analysis of functional T-cell memory against DENV and are able to correlate this with HLA alleles expressed in the very same donors. Collectively, the data suggest an HLA-linked protective role of CD8⁺ T-cell responses and do not support a causative role for CD8⁺ T cells in the induction of severe disease following secondary heterologous infection.     

Adenosine dialdehyde and nitrous oxide induce HL-60 differentiation

Adenosine dialdehyde and nitrous oxide, specific S-adeno- sylhomocysteine hydrolase and methionine synthetase inhibitors, respectively, induced differentiation of the human promyelocytic cell line HL-60. Their effect did not appear to be mediated through changes in transmethylation or decreased S-adenosylmethionine synthesis because (1) there was little correlation between the concentrations of adenosine dialdehyde that induced differentiation and those that changed the ratio of the intracellular concentrations of S- adenosylmethionine to S-adenosylhomocysteine, and (2) inhibition of methionine adenosyltransferase by cycloleucine did not induce differentiation. The differentiation induced by adenosine dialdehyde was prevented by homocysteine and that by nitrous oxide was inversely related to the medium methionine concentration. This suggested that differentiation was secondary to decreased methionine synthesis.