David I. Hong

T cell receptor ligation induces the formation of dynamically regulated signaling assemblies

Tcell antigen receptor (TCR) ligation initiates tyrosine kinase activation, signaling complex assembly, and immune synapse formation. Here, we studied the kinetics and mechanics of signaling complex formation in live Jurkat leukemic T cells using signaling proteins fluorescently tagged with variants of enhanced GFP (EGFP). Within seconds of contacting coverslips coated with stimulatory antibodies, T cells developed small, dynamically regulated clusters which were enriched in the TCR, phosphotyrosine, ZAP-70, LAT, Grb2, Gads, and SLP-76, excluded the lipid raft marker enhanced yellow fluorescent protein–GPI, and were competent to induce calcium elevations. LAT, Grb2, and Gads were transiently associated with the TCR. Although ZAP-70–containing clusters persisted for more than 20 min, photobleaching studies revealed that ZAP-70 continuously dissociated from and returned to these complexes. Strikingly, SLP-76 translocated to a perinuclear structure after clustering with the TCR. Our results emphasize the dynamically changing composition of signaling complexes and indicate that these complexes can form within seconds of TCR engagement, in the absence of either lipid raft aggregation or the formation of a central TCR-rich cluster.

Involvement of CRAF1, a relative of TRAF, in CD40 signaling

CD40 is a receptor on the surface of B lymphocytes, the activation of which leads to B cell survival, growth, and differentiation. A yeast two-hybrid screen identified a gene, CRAF1, encoding a protein that interacts directly with the CD40 cytoplasmic tail through a region of similarity to the tumor necrosis factor-alpha (TNF-alpha) receptor-associated factors. Overexpression of a truncated CRAF1 gene inhibited CD40-mediated up-regulation of CD23. A region of CRAF1 was similar to the TNF-alpha receptor-associated factors TRAF1 and TRAF2 and so defined a shared TRAF-C domain that was necessary and sufficient for CD40 binding and homodimerization. The CRAF1 sequence also predicted a long amphipathic helix, a pattern of five zinc fingers, and a zinc ring finger. It is likely that other members of the TNF receptor superfamily use CRAF-related proteins in their signal transduction processes.

Hypersensitivity reactions to chemotherapy: Outcomes and safety of rapid desensitization in 413 cases

BACKGROUND Hypersensitivity reactions (HSRs) to chemotherapeutic drugs, including mAbs, often require that the provoking medication be discontinued, thus raising a dilemma for the caregiver: further use could precipitate a severe, even fatal, allergic reaction on re-exposure, but alternative drugs might be poorly tolerated or much less effective compared with the preferred agent. OBJECTIVE We have developed a standardized rapid desensitization protocol for achieving temporary tolerization to drug allergens. In this study we evaluate the safety and efficacy of this protocol. METHODS Ninety-eight patients who had HSRs in response to treatment with carboplatin, cisplatin, oxaliplatin, paclitaxel, liposomal doxorubicin, doxorubicin, or rituximab received rapid desensitization to these agents. A standardized 12-step protocol was used, with treatment given intravenously or intraperitoneally. Initial desensitizations occurred in the medical intensive care unit, whereas most subsequent infusions took place in an outpatient setting. Safety and efficacy of the protocol were assessed by review of treatment records. RESULTS Of the 413 desensitizations performed, 94% induced mild or no reactions. No life-threatening HSRs or deaths occurred during the procedure, and all patients received their full target dose. Most reactions occurred during the first desensitization. Reactions were most commonly reported at the last step of the protocol. Desensitizations through the intravenous and intraperitoneal routes were equally effective. CONCLUSIONS Our standardized 12-step protocol for rapid drug desensitization is safe and effective and has been adopted as the standard of care at our institutions in treating patients with HSRs to chemotherapeutic drugs, including mAbs.

Persistence of Cooperatively Stabilized Signaling Clusters Drives T-Cell Activation

ABSTRACT Antigen recognition triggers the recruitment of the critical adaptor protein SLP-76 to small macromolecular clusters nucleated by the T-cell receptor (TCR). These structures develop rapidly, in parallel with TCR-induced increases in tyrosine phosphorylation and cytosolic calcium, and are likely to contribute to TCR-proximal signaling. Previously, we demonstrated that these SLP-76-containing clusters segregate from the TCR and move towards the center of the contact interface. Neither the function of these clusters nor the structural requirements governing their persistence have been examined extensively. Here we demonstrate that defects in cluster assembly and persistence are associated with defects in T-cell activation in the absence of Lck, ZAP-70, or LAT. Clusters persist normally in the absence of phospholipase C-γ1, indicating that in the absence of a critical effector, these structures are insufficient to drive T-cell activation. Furthermore, we show that the critical adaptors LAT and Gads localize with SLP-76 in persistent clusters. Mutational analyses of LAT, Gads, and SLP-76 indicated that multiple domains within each of these proteins contribute to cluster persistence. These data indicate that multivalent cooperative interactions stabilize these persistent signaling clusters, which may correspond to the functional complexes predicted by kinetic proofreading models of T-cell activation.

UPSTREAM TRNA GENES ARE ESSENTIAL FOR EXPRESSION OF SMALL NUCLEAR AND CYTOPLASMIC RNA GENES IN TRYPANOSOMES

An interesting feature of trypanosome genome organization involves genes transcribed by RNA polymerase III. The U6 small nuclear RNA (snRNA), U-snRNA B (the U3 snRNA homolog), and 7SL RNA genes are closely linked with different, divergently oriented tRNA genes. To test the hypothesis that this association is of functional significance, we generated deletion and block substitution mutants of all three small RNA genes and monitored their effects by transient expression in cultured insect-form cells of Trypanosoma brucei. In each case, two extragenic regulatory elements were mapped to the A and B boxes of the respective companion tRNA gene. In addition, the tRNA(Thr) gene, which is upstream of the U6 snRNA gene, was shown by two different tests to be expressed in T. brucei cells, thus confirming its identity as a gene. This association between tRNA and small RNA genes appears to be a general phenomenon in the family Trypanosomatidae, since it is also observed at the U6 snRNA loci in Leishmania pifanoi and Crithidia fasciculata and at the 7SL RNA locus in L. pifanoi. We propose that the A- and B-box elements of small RNA-associated tRNA genes serve a dual role as intragenic promoter elements for the respective tRNA genes and as extragenic regulatory elements for the linked small RNA genes. The possible role of tRNA genes in regulating small RNA gene transcription is discussed.

Allergy to monoclonal antibodies: cutting-edge desensitization methods for cutting-edge therapies

Monoclonal antibodies are important therapeutic tools, but their usefulness is limited in patients who experience acute infusion reactions, most of which are consistent with type I hypersensitivity reactions including anaphylaxis. Patients who experience acute infusion reactions face the prospect of stopping treatment or switching to an alternative, and potentially more toxic or inferior treatment. Another option that overcomes the treatment hurdle of these reactions is rapid desensitization, a procedure in which the offending agent is re-administered in a step-wise, highly controlled fashion. While the risk of reactions is not completely eliminated, desensitization has proven to be a highly effective re-administration strategy for most patients who otherwise would not be able to tolerate their monoclonal antibody therapy owing to drug-induced anaphylaxis. This article reviews the current literature on desensitization and other readministration protocols to monoclonal antibodies with an emphasis on four agents: rituximab, infliximab, cetuximab and trastuzumab.

Safety, Costs, and Efficacy of Rapid Drug Desensitizations to Chemotherapy and Monoclonal Antibodies

BACKGROUND Rapid drug desensitization (RDD) is used to address hypersensitivity reactions to chemotherapeutics and monoclonal antibodies, allowing patients to be treated with optimal pharmacological agents. RDD protocols are tailored to each individual patients reaction and needs, and protect against anaphylaxis, but overall risks, costs, and benefits have not been determined. OBJECTIVE We investigated the safety, efficacy, costs, and life expectancy of patients in a large population undergoing RDD. METHODS We analyzed 2177 RDD procedures performed in 370 patients with cancer, vasculitis, and hematological and connective tissue diseases who presented 402 reactions. A subgroup of carboplatin allergic patients with ovarian cancer treated with RDD was analyzed for costs and life expectancy and compared with a nonallergic control group. RESULTS RDD allowed all patients to receive safely the full dose of the medication to which they were reactive. A gradual increase in the fraction of outpatient desensitizations from 81% to 98% was achieved through risk stratification. Of the 2177 desensitizations, 93% had no or mild reactions whereas 7% had moderate to severe reactions, which did not preclude the completion of the treatment, and there were no deaths. Overall health costs in the carboplatin allergic group were not higher than those in the nonallergic group treated with standard of care. Administration of carboplatin through RDD was as effective as standard administration with a nonsignificant increase in life expectancy in desensitized patients as compared with nonallergic, nondesensitized controls. CONCLUSIONS RDD is cost effective and safe for allergic patients with cancer and chronic disease to remain on first line therapy.

Inhibition of Th2 adaptive immune responses and pulmonary inflammation by leukocyte Ig-like receptor B4 on dendritic cells.

We previously established that the inhibitory receptor LILRB4 mitigates LPS-induced, neutrophil-dependent pathologic effector mechanisms in inflammation. We now report that LILRB4 on dendritic cells (DCs) counterregulates development of an adaptive Th2 immune response and ensuing inflammation in a model of allergic pulmonary inflammation, initiated by inhalation sensitization with OVA and LPS followed by airway challenge with OVA. We found that Lilrb4−/− mice had significantly exacerbated eosinophilic pulmonary inflammation, as assessed in bronchoalveolar lavage and lung tissue, as well as elevated levels of OVA-specific IgE and Th2 cytokines produced by OVA-restimulated lymph node cells. LILRB4 was preferentially expressed on MHC class IIhighCD86high OVA-bearing DCs in lung-draining lymph nodes after sensitization or challenge. Moreover, the lymph nodes of Lilrb4−/− mice had significantly more of these mature DCs after challenge with OVA, which was accompanied by significantly more IL-4–producing lymphocytes, compared with Lilrb4+/+ mice. Sensitization of naive Lilrb4+/+ mice by transfer of OVA-LPS-pulsed Lilrb4−/− bone marrow-derived DCs was sufficient to confer exacerbated allergic lung pathology upon challenge with OVA, compared with mice that received Lilrb4+/+ bone marrow-derived DCs. Our findings establish that maturation and migration of pulmonary DCs to lymph nodes in response to Ag and an innate immune stimulus is associated with upregulated expression of LILRB4. In addition, this receptor attenuates the number of these mature DCs and attendant IL-4–producing lymphocytes in the lymph nodes, and accordingly, the ability of DCs to elicit pathologic Th2 pulmonary inflammation.

Immediate Drug Hypersensitivity

Drug allergy affects a large percentage of the general population. A listed drug allergy can also have broad implications for many aspects of patient care. Here, we will review recent advances in the arena of drug allergies with a focus on antibiotics, monoclonals, NSAIDs, and chemotherapeutics.