A22 USING INTESTINAL ORGANOIDS TO CHARACTERIZE THE NAIP-NLRC4 INFLAMMASOME RESPONSE IN THE INTESTINAL EPITHELIUM

Background

The NAIP-NLRC4 inflammasome is an important innate defence mechanism in intestinal epithelial cells (IECs) that protects the gut from invasive pathogens. NAIP-NLRC4 activation triggers pyroptotic cell death, releases active interleukin (IL)-18, and promotes the expulsion of infected enterocytes. Dysregulated inflammasomes result in exaggerated inflammation of the intestinal mucosa which is characterisitic of inflammatory bowel disease (IBD). There is increasing evidence that inflammasomes in IEC behave differently than in immune cells. However, a majority of inflammasome pathway characterization is studied immune cells. In addition, NAIP-NLRC4 activity in macrophages has been shown to be important for regulating the expression of nitric oxide (Nos2). The potential transcriptomic impact of NAIP-NLRC4 activity in IECs has yet to be explored.

Purpose

We will use intestinal orgnaoids to systematically characterize the NAIP-NLRC4 inflammasome pathway and identify the transcriptomic impact of NAIP-NLRC4 activity in IECs. To better define the role of NAIP-NLRC4 activity during a physiological infection, we have developed a novel ex vivo model of Shigella infection in 3D organoids.

Method

Organoids were derived from the ileal crypts of wild type (WT) and Nlrc4^-/-, Casp1^-/-, Pycard^-/-, or Tlr5^-/- mice and stimulated with Pam3CSk4, LPS, or flagellin. Inflammasome activation was assessed by Western blot (WB) and propidium iodide uptake. WT and Nlrc4^-/- organoids were infected with WT or a non-invasive Shigella mutant and the inflammasome response was evaluated by WB and a colony forming unit assay. WT and Nlrc4^-/- organoids were stimulated with flagellin and gene expression was assessed by RT-qPCR.

Result(s)

Basolateral organoid stimulation with bacterial ligands revealed a novel response of IECs to bacterial flagellin that results in pyroptosis and IL-18 processing. Basolateral internalization of flagellin occurred in a TLR5-independent manner. Inflammasome activation by flagellin was fully abrogated in Nlrc4^-/- and Casp1^-/- organoids while only IL-18 processing was affected in Pycard^-/- organoids. Infection with only WT Shigella induced inflammasome activation in an NLRC4-dependent manner. Interestingly, flagellin stimulation of WT but not Nlrc4^-/- organoids led to increased expression of Nos2. Furthermore, Nlrc4^-/- organoids had significantly lower expression levels of cytokine genes Ccl20, Cxcl1, and Tnf following inflammasome activation.

Conclusion(s)

Our study demonstrates an integral role for epithelial NAIP-NLRC4 inflammasomes in the response to bacterial flagellin and Shigella infection. We have uncovered a novel response of IECs to basolateral flagellin stimulation and revealed that NAIP-NLRC4 is important for the transcriptional regulation of inflammatory genes. Further work will examine how NAIP-NLRC4 activation controls inflammation and epithelial integrity by analyzing the NLRC4-dependent transcriptome and the effects on cell proliferation, differentiation, and barrier integrity.

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CCC, CIHR

Disclosure of Interest

None Declared

A Randomised Phase II Clinical Trial Comparing the Deliverability and Acute Toxicity of Wide Tangent versus Volumetric Modulated Arc Therapy to the Breast and Internal Mammary Chain

AIMS

Inclusion of the internal mammary chain in the radiotherapy target volume (IMC-RT) improves disease-free and overall survival in higher risk breast cancer patients, but increases radiation doses to heart and lungs. Dosimetric data show that either modified wide-tangential fields (WT) or volumetric modulated arc therapy (VMAT) together with [AQ1]voluntary deep inspiration breath hold (vDIBH) keep mean heart doses below 4 Gy in most patients. However, the impact on departmental resources has not yet been documented. This phase II clinical trial compared the time taken to deliver IMC-RT using either WT and vDIBH or VMAT and vDIBH, together with planning time, dosimetry, set-up reproducibility and toxicity.

MATERIALS AND METHODS

Left-sided breast cancer patients requiring IMC-RT were randomised to receive either WT(vDIBH) or VMAT radiotherapy. The primary outcome was treatment time, powered to detect a minimum difference of 75 min (5 min/fraction) between techniques. The population mean displacement, systematic error and random error for cone beam computed tomography chest wall matches in three directions of movement were calculated. Target volume and organ at risk doses were compared between groups. Side-effects, including skin (Radiation Therapy Oncology Group), lung and oesophageal toxicity (Common Terminology Criteria for Adverse Events v 4.03) rates, were compared between the groups over 3 months. Patient-reported outcome measures, including shoulder toxicity at baseline, 6 months and 1 year, were compared.

RESULTS

Twenty-one patients were recruited from a single UK centre between February 2017 and January 2018. The mean (standard deviation) total treatment time per fraction for VMAT treatments was 13.2 min (1.7 min) compared with 28.1 min (3.3 min) for WT(vDIBH). There were no statistically significant differences in patient set-up errors in between groups. The average mean heart dose for WT(vDIBH) was 2.6 Gy compared with 3.4 Gy for VMAT(vDIBH) (P = 0.13). The mean ipsilateral lung V17Gy was 32.8% in the WT(vDIBH) group versus 34.4% in the VMAT group (P = 0.2). The humeral head (mean dose 16.8 Gy versus 2.8 Gy), oesophagus (maximum dose 37.3 Gy versus 20.1 Gy) and thyroid (mean dose 22.0 Gy versus 11.2 Gy) all received a statistically significantly higher dose in the VMAT group. There were no statistically significant differences in skin, lung or oesophageal toxicity within 3 months of treatment. Patient-reported outcomes of shoulder toxicity, pain, fatigue, breathlessness and breast symptoms were similar between groups at 1 year.

CONCLUSION

VMAT(vDIBH) and WT(vDIBH) are feasible options for locoregional breast radiotherapy including the IMC. VMAT improves nodal coverage and delivers treatment more quickly, resulting in less breath holds for the patient. This is at the cost of increased dose to some non-target tissues. The latter does not appear to translate into increased toxicity in this small study.

Fueling Machine Model for Simulation of Spent Fuel Behavior in Postulated Fuel Handling Accidents

On-power fueling is an important feature of the CANDU® reactor. Fueling is a routine operation with a large number of channel fueling visits made each year with the fueling machines acting as the key system. Hence, safety analysis must consider fueling machine events typically when the fueling machine is in transit toward the spent fuel port. This paper presents a model of fueling machine containing spent fuel with complex configuration and multiprocess mechanisms. Using an integral approach with fuel and fueling machine, this model tends to improve previous modeling method, which only takes account of a slice of fuel or fueling machine. This fueling machine model is developed for simulations of the fueling machine coolant thermal hydraulics behavior, the spent fuel behavior, and potential fission product release during postulated loss of heat removal accidents. An example of its application is also presented in this paper.

Abstract OT2-07-06: Antibody-coupled T cell receptor (ACTR) engineered autologous T cells in combination with trastuzumab for the treatment of HER2-positive malignancies

Antibody-Coupled T cell Receptor (ACTR) is an autologous engineered T cell therapy developed to combine with tumor-targeting antibodies to exert potent anti-tumor immune responses and tumor cell killing. The ACTR construct is composed of the extracellular domain of CD16 fused to CD3ζ signaling and T cell co-stimulatory domains. ACTR-expressing T cells are universal in that they can be paired with a therapeutic antibody to target specific antigens on tumors. Unum has two ACTR constructs, ACTR087 and ACTR707, currently in clinical testing. ACTR087 and ACTR707 are being tested in combination with rituximab in subjects with CD20+ B cell lymphoma in two separate trials (NCT02776813 and NCT03189836, respectively). Preliminary data with ACTR087 + rituximab has demonstrated clinical proof-of-concept and a dose-response relationship in subjects with relapsed/refractory B cell lymphoma. ACTR087 is also being tested in combination with a novel BCMA-targeting antibody in subjects with multiple myeloma (NCT03266692).

While T cell therapies, such as chimeric antigen receptor (CAR) T cells, have demonstrated clinical activity in hematological cancers, the therapeutic potential of this approach has yet to be established in solid tumors. Challenges associated with targeting solid tumors with CAR-T cells include tumor antigen heterogeneity and antigen expression on normal tissues. HER2 is a well-established therapeutic target that is over-expressed in a number of cancer indications. HER2 is also expressed at low levels on normal epithelial cells, creating a risk for on-target/off-tumor toxicities of HER2-targeted CAR-T cells. Here we present nonclinical studies demonstrating that ACTR T cells in combination with trastuzumab have antigen density-dependent activity on HER2-expressing tumor cell lines, while trastuzumab-based CAR-T cells do not. We observed that ACTR + trastuzumab had robust activity against HER2-amplified tumor cells and more modest activity against non-amplified tumor cells, whereas HER2-targeting CAR-T cells had comparable activity against HER2-amplified and non-amplified tumor cells. On normal human primary cells, ACTR + trastuzumab had minimal activity in comparison to HER2 CAR-T cells, suggesting that ACTR + trastuzumab may exhibit a superior clinical therapeutic index. Furthermore, the activity of ACTR T cells against HER2-amplified tumor cells was titratable with antibody concentration, allowing for control of ACTR activity by modulation of trastuzumab concentration. Together, these data demonstrate the specificity of the ACTR T cell therapeutic approach to target HER2-amplified tumors and support clinical testing in combination with trastuzumab.

A phase 1, multicenter, single-arm, open-label dose escalation study, ATTCK-34-01, is proposed to evaluate ACTR T cells in combination with trastuzumab in subjects with advanced HER2-positive malignancies. The primary study objectives are to assess the safety and tolerability of the combination, and to define the recommended phase 2 dose combination for further study. Additional objectives include assessment of anti-tumor activity, ACTR T cell persistence and trastuzumab pharmacokinetics. Enrollment is expected to commence in early 2019.

Citation Format: O'Callaghan KM, Shin J, Cheung AS, Cheema T, Judge C, Ranger A, Huet HA, Ettenberg SA, Sachs J, Vasconcelles M, Motz G. Antibody-coupled T cell receptor (ACTR) engineered autologous T cells in combination with trastuzumab for the treatment of HER2-positive malignancies [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT2-07-06.

Evaluation of a Novel Field-placement Algorithm for Locoregional Breast Cancer Radiotherapy Including the Internal Mammary Chain

AIMS

Irradiation of the internal mammary chain (IMC) is increasing following recently published data, but the need for formal delineation of lymph node volumes is slowing implementation in some healthcare settings. A field-placement algorithm for irradiating locoregional lymph nodes including the IMC could reduce the resource impact of introducing irradiation of the IMC. This study describes the development and evaluation of such an algorithm.

MATERIALS AND METHODS

An algorithm was developed in which six points representing lymph node clinical target volume borders (based on European Society for Radiotherapy and Oncology consensus nodal contouring guidelines) were placed on computed tomography-defined anatomical landmarks and used to place tangential and nodal fields. Single-centre testing in 20 cases assessed the success of the algorithm in covering planning target volumes (PTVs) and adequately sparing organs at risk. Plans derived using the points algorithm were also compared with plans generated following formal delineation of nodal PTVs, using the Wilcoxon signed rank test. Timing data for point placement were collected. Multicentre testing using the same methods was then carried out to establish whether the technique was transferable to other centres.

RESULTS

Single-centre testing showed that 95% of cases met the nodal PTV coverage dose constraints (binomial probability confidence interval 75.1-99.9%) with no statistically significant reduction in mean heart dose or ipsilateral lung V17Gy associated with formal nodal delineation. In multicentre testing, 69% of cases met nodal PTV dose constraints and there was a statistically significant difference in IMC PTV coverage using the points algorithm when compared with formally delineated nodal volumes (P < 0.01). However, there was no difference in axillary level 1-4 PTV coverage (P = 0.11) with all cases meeting target volume constraints.

CONCLUSIONS

The optimal strategy for breast and locoregional lymph node radiotherapy is target volume delineation. However, use of this novel points-based field-placement algorithm results in dosimetrically acceptable plans without the need for formal lymph node contouring in a single-centre setting and for the breast and level 1-4 axilla in a multicentre setting. Further quality assurance measures are needed to enable implementation of the algorithm for irradiation of the IMC in a multicentre setting.

Physiological and emotional effects of pentatonic live music played for preterm neonates and their mothers in the Newborn Intensive Care Unit: A randomized controlled trial

OBJECTIVE

Despite attempts to increase calmness in the Newborn Intensive Care Unit (NICU), preterm neonates still experience stress. The question arises how to further promote the infants' wellbeing. Therefore, the immediate effects of pentatonic live music on preterm infants and their mothers were examined.

DESIGN AND METHODS

In a two-centre randomized controlled trial with crossover design preterm infants were exposed sequentially to two conditions: live pentatonic harp music (LPHM) used in Anthroposophic Medicine or standard care. The order of the conditions was randomized within each subject. The primary outcome was change of the number of oxygen desaturations < 90%/h, whereas secondary outcomes were: heart rate, respiratory rate, oxygen saturation, heart rate variability (HRV), the perfusion index, pulse-transit-time and maternal anxiety and others not reported on in this article.

RESULTS

21 preterm infants were randomized (14 girls), mean gestational age at measurement 35 + 0 weeks (SD 1 week). The primary outcome parameter showed no significant changes. Regarding the secondary outcomes the comparison of the pre-post-differences between the conditions showed significant effects for the HRV parameters pNN₅₀ (ΔpNN₅₀ = 1.46%, z = -2.47, p =  .001) and SDNN (ΔSDNN=-0.06 ms, z = -2.25, p =  .002). The music intervention significantly increased the values of pNN₅₀ (Mdn 1.2% vs. 2.6%, p =  0.04) and marginally those of SDNN (Mdn 31.7 ms vs. 36.4 ms, p =  0.05). No changes were found in the other parameters.

CONCLUSIONS

While the use of music in the NICU had no effect on the number of oxygen desaturations, it increased two HRV parameters indicative of infants' parasympathetic tone.

A Dosimetric Comparison of Breast Radiotherapy Techniques to Treat Locoregional Lymph Nodes Including the Internal Mammary Chain

AIMS

Radiotherapy target volumes in early breast cancer treatment increasingly include the internal mammary chain (IMC). In order to maximise survival benefits of IMC radiotherapy, doses to the heart and lung should be minimised. This dosimetry study compared the ability of three-dimensional conformal radiotherapy, arc therapy and proton beam therapy (PBT) techniques with and without breath-hold to achieve target volume constraints while minimising dose to organs at risk (OARs).

MATERIALS AND METHODS

In 14 patients' datasets, seven IMC radiotherapy techniques were compared: wide tangent (WT) three-dimensional conformal radiotherapy, volumetric-modulated arc therapy (VMAT) and PBT, each in voluntary deep inspiratory breath-hold (vDIBH) and free breathing (FB), and tomotherapy in FB only. Target volume coverage and OAR doses were measured for each technique. These were compared using a one-way ANOVA with all pairwise comparisons tested using Bonferroni's multiple comparisons test, with adjusted P-values ≤ 0.05 indicating statistical significance.

RESULTS

One hundred per cent of WT(vDIBH), 43% of WT(FB), 100% of VMAT(vDIBH), 86% of VMAT(FB), 100% of tomotherapy FB and 100% of PBT plans in vDIBH and FB passed all mandatory constraints. However, coverage of the IMC with 90% of the prescribed dose was significantly better than all other techniques using VMAT(vDIBH), PBT(vDIBH) and PBT(FB) (mean IMC coverage ± 1 standard deviation = 96.0% ± 4.3, 99.8% ± 0.3 and 99.0% ± 0.2, respectively). The mean heart dose was significantly reduced in vDIBH compared with FB for both the WT (P < 0.0001) and VMAT (P < 0.0001) techniques. There was no advantage in target volume coverage or OAR doses for PBT(vDIBH) compared with PBT(FB).

CONCLUSIONS

Simple WT radiotherapy delivered in vDIBH achieves satisfactory coverage of the IMC while meeting heart and lung dose constraints. However, where higher isodose coverage is required, VMAT(vDIBH) is the optimal photon technique. The lowest OAR doses are achieved by PBT, in which the use of vDIBH does not improve dose statistics.

Pregnancy in type 2B VWD: a case series

Type 2B von Willebrand disease (VWD) is a rare, inherited bleeding disorder resulting from a qualitative defect in von Willebrand factor (VWF). There is very little published information on how to quantify bleeding risk and manage haemostasis in type 2B VWD patients during pregnancy. This article presents the changes in VWF parameters and details of patient management and delivery outcomes for four pregnancies in three women with two different mutations causing type 2B VWD. We report an unexpected rise in the VWF:Ag at 37 weeks gestation in two sisters with R1306W associated with significant thrombocytopenia. These patients were supported with platelet transfusions as well as intermediate purity VWF-FVIII plasma concentrates during the peri- and postpartum periods. No thrombocytopenia was observed in our third case with a mutation encoding an R1308C substitution; haemostatic support was with intermediate purity VWF-FVIII plasma concentrates alone. No adverse bleeding events occurred and in all cases a live healthy infant was delivered. One patient was readmitted post partum with bleeding symptoms due to retained placenta; no further haemostatic support was given at this time. This case series is the first to detail the progression of laboratory parameters, management and outcomes of pregnancy in patients with type 2B VWD. The cases illustrate some of the challenges posed by the increased production of a VWF variant with a gain-of-function effect. The rapid coagulation changes observed in this series illustrate the need for continual monitoring of VWF parameters and platelet count throughout pregnancy in women with type 2B VWD.

Histone H3 phosphorylation in the rat pineal gland: adrenergic regulation and diurnal variation

In this study, we investigated phosphorylation of Ser10 in histone H3 by norepinephrine (NE) in the rat pineal gland. In whole-animal studies, we demonstrated a marked increase in histone H3 phosphorylation in the rat pineal gland during the first half of the dark period. Exposure to light during this period caused a rapid decline in histone H3 phosphorylation with an estimated t1/2 of less than 15 min, indicating a high level of dephosphorylation activity. Corresponding studies in cultured pineal cells revealed that treatment with NE produced an increase in histone H3 phosphorylation that peaked between 2 and 3 h and declined rapidly by 4 h. The NE-induced histone H3 phosphorylation was blocked by cotreatment with propranolol or KT5720, a protein kinase A inhibitor, but not by prazosin or other kinase inhibitors. Moreover, only treatment with dibutyryl cAMP but not other kinase activators mimicked the effect of NE on histone H3 phosphorylation. The NE-stimulated H3 phosphorylation was markedly increased by cotreatment with a serine/threonine phosphatase inhibitor, tautomycin or okadaic acid, supporting a high level of ongoing histone H3 dephosphorylation activity. Together, our results indicate that histone H3 phosphorylation is a naturally occurring event at night in the rat pineal gland that is driven almost exclusively by a NE-->beta-adrenergic-->cAMP/protein kinase A signaling mechanism. This transient histone H3 phosphorylation probably reflects the nocturnal activation of multiple adrenergic-regulated genes in the rat pineal gland.

Spontaneous spinal epidural hematoma in an 11-month-old girl

An 11-month-old girl was admitted for a 2-month history of regression of motor milestones and lateralizing neurologic findings. Tests for hypercoagulability were all within normal limits except for a moderately elevated fibrinogen level. Urine and blood cultures were negative for growth. Complete MRI of the spine revealed a well-defined extradural inhomogeneous signal intensity extending from C(4) to T(3) suggestive of a subacute hematoma with evidence of evolving hemorrhagic change. There was no evidence of underlying arterial venous fistula or malformation. She underwent a cervicothoracic laminoplasty and evacuation of the hematoma. The clot was confirmed to be a hematoma on pathologic investigation. She made an uneventful recovery with gradual return of neurologic function. This case represents the longest known duration between initial symptoms and definitive management of spontaneous spinal epidural hematoma.

Single amino acid mutations in the murine MHC class II A beta cytoplasmic domain abrogate antigen presentation

Class II MHC molecules are heterodimeric transmembrane glycoproteins that function in the presentation of Ag to CD4+ T cells. Deletion of the cytoplasmic domains of the murine class II A alpha- and A beta-chains has previously been shown to diminish Ag presentation and abrogate rejection of class II-transfected tumor cells. To examine the contributions of individual amino acid residues of the A beta cytoplasmic domain to Ag presentation and tumor rejection, we have produced a series of cell lines expressing A beta class II molecules with site-directed mutations. An A beta(k) cDNA was constructed with mutations in the five conserved amino acid residues, Q224, K225, L235, L236, and Q237 (delta5). In addition, cDNA were produced in which alanine was individually substituted for A beta(k) cytoplasmic domain residues 224 through 237 or doubly substituted at residues G226 and P227 or L235 and L236. These mutant cDNAs were individually cotransfected with wild-type A alpha cDNA into the class II-negative M12.C3 B lymphoma and Sal sarcoma cell lines. As was previously reported for transfectants lacking the entire A beta(k) cytoplasmic domain, the delta5 M12.C3 transfectant could not effectively present Ag to an autoreactive Ak-restricted T cell hybrid, and the delta5 Sal transfectant was not rejected when inoculated into syngeneic hosts. A finer analysis revealed that alteration of the individual residue Q224 or the two residues G226 and P227 abrogated Ag presentation in vitro, while mutation of G226 diminished tumor rejection in vivo. Thus, the function of the A beta cytoplasmic domain in Ag presentation both in vitro and in vivo can be disturbed by mutation of single amino acid residues.

Single amino acid mutations in the murine MHC class II A beta cytoplasmic domain abrogate antigen presentation

Class II MHC molecules are heterodimeric transmembrane glycoproteins that function in the presentation of Ag to CD4+ T cells. Deletion of the cytoplasmic domains of the murine class II A alpha- and A beta-chains has previously been shown to diminish Ag presentation and abrogate rejection of class II-transfected tumor cells. To examine the contributions of individual amino acid residues of the A beta cytoplasmic domain to Ag presentation and tumor rejection, we have produced a series of cell lines expressing A beta class II molecules with site-directed mutations. An A beta(k) cDNA was constructed with mutations in the five conserved amino acid residues, Q224, K225, L235, L236, and Q237 (delta5). In addition, cDNA were produced in which alanine was individually substituted for A beta(k) cytoplasmic domain residues 224 through 237 or doubly substituted at residues G226 and P227 or L235 and L236. These mutant cDNAs were individually cotransfected with wild-type A alpha cDNA into the class II-negative M12.C3 B lymphoma and Sal sarcoma cell lines. As was previously reported for transfectants lacking the entire A beta(k) cytoplasmic domain, the delta5 M12.C3 transfectant could not effectively present Ag to an autoreactive Ak-restricted T cell hybrid, and the delta5 Sal transfectant was not rejected when inoculated into syngeneic hosts. A finer analysis revealed that alteration of the individual residue Q224 or the two residues G226 and P227 abrogated Ag presentation in vitro, while mutation of G226 diminished tumor rejection in vivo. Thus, the function of the A beta cytoplasmic domain in Ag presentation both in vitro and in vivo can be disturbed by mutation of single amino acid residues.

Mitogen-activated protein kinase-mediated Fas apoptotic signaling pathway

Ligation of the cell surface receptor Fas/APO-1 (CD95) by its specific ligand or by anti-Fas antibodies rapidly induces apoptosis in susceptible cells. To characterize the molecular events involved in Fas-induced apoptosis, we examined the contribution of two subgroups of the mitogen-activated protein (MAP) kinase family, the Jun kinases or stress-activated protein kinases (JNKs/SAPKs) and the extracellular signal-regulated kinases (ERKs), in a Fas-sensitive neuroblastoma cell line. Here we show that both JNK and ERK protein kinases were activated upon Fas crosslinking through a Ras-dependent mechanism. Interference with either the JNK or ERK pathway by ectopic expression of dominant-interfering mutant proteins blocked Fas-mediated apoptosis. ERK activation was transient and associated with induced expression of the Fas receptor. In contrast, JNK activation was sustained and correlated with the onset of apoptosis. These data indicate that the ERK and the JNK groups of MAP kinases cooperate in the induction of cell death by Fas. Inhibition of Fas killing by an interleukin 1beta-converting enzyme (ICE)-like protease inhibitor peptide did not modify Fas-induced JNK activation upon Fas ligation. In contrast, changes in Bcl-2 level due to expression of sense and antisense vectors influenced the sensitivity to Fas killing and Fas-induced JNK activation.

Crossreacting human lymphoma idiotypes

We have examined an unselected series of 72 lymphomas of diverse histologies with a panel of mouse monoclonal antibodies specific for human B-lymphoma-derived Ig idiotypes (anti-ids) to determine the nature and extent of id/anti-id crossreactivity. The anti-id antibodies were prepared from Ig isolated from seven follicular center cell lymphomas by heterohybridoma technique. Thirty-six of 75 individual anti-ids obtained in this manner were further selected based on their reactivity with highly restricted or private idiotypic determinants. Twelve of the 72 (17%) lymphoma biopsies reacted with one or more of the 36 anti-ids that detect private determinants. A pool consisting of five individual antibodies would have detected 11 of the 12 crossreacting tumors. Staining of tumor cell populations was homogeneous in the positive cases, suggesting uniform idiotype expression. If there was a segregated staining pattern, it was generally related to the presence of CD3+ T cells in the section. These follicular center cell-derived anti-ids cross-reacted with follicular center cell tumors of all histologic grades with frequencies ranging from 13% to 50%. The structural basis for the crossreactivity of our lymphoma-derived private anti-ids is as yet not known. However, the reactivity of certain anti-ids with both kappa- and lambda-expressing tumors suggests a biased use of V gene segments in these crossreactive clones that is probably related to the VH gene. These data suggest the possibility that lymphoma may develop in a highly restricted pool of normal differentiated B cells or in B-cell subsets that express a limited repertoire of unmutated VH gene segments.