Synthetic cationic helical polypeptides for the stimulation of antitumour innate immune pathways in antigen-presenting cells

Intracellular DNA sensors regulate innate immunity and can provide a bridge to adaptive immunogenicity. However, the activation of the sensors in antigen-presenting cells (APCs) by natural agonists such as double-stranded DNAs or cyclic nucleotides is impeded by poor intracellular delivery, serum stability, enzymatic degradation and rapid systemic clearance. Here we show that the hydrophobicity, electrostatic charge and secondary conformation of helical polypeptides can be optimized to stimulate innate immune pathways via endoplasmic reticulum stress in APCs. One of the three polypeptides that we engineered activated two major intracellular DNA-sensing pathways (cGAS-STING (for cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes) and Toll-like receptor 9) preferentially in APCs by promoting the release of mitochondrial DNA, which led to the efficient priming of effector T cells. In syngeneic mouse models of locally advanced and metastatic breast cancers, the polypeptides led to potent DNA-sensor-mediated antitumour responses when intravenously given as monotherapy or with immune checkpoint inhibitors. The activation of multiple innate immune pathways via engineered cationic polypeptides may offer therapeutic advantages in the generation of antitumour immune responses.

Institution-Wide Retreats Foster Organizational Learning and Action at a Comprehensive Cancer Center

Providing safe and informed healthcare for sexual and gender minority (SGM) individuals with cancer is stymied by the lack of sexual orientation and gender identity (SOGI) data reliably available in health records and by insufficient training for staff. Approaches that support institutional learning, especially around sensitive topics, are essential for hospitals seeking to improve practices impacting patient safety and research. We engineered annual institutional retreats to identify and unify stakeholders, promote awareness of gaps and needs, identify initiatives, minimize redundant projects, and coordinate efforts that promote improvements in SGM cancer care, education, and research. The 2022 and 2023 retreats employed a 4-h hybrid format allowing virtual and in-person engagement. Retreat organizers facilitated small-group discussions for brainstorming among participants. We performed descriptive statistics from retreat evaluations. The retreats engaged 104 attendees from distinct departments and roles. Participants expressed robust satisfaction, commending the retreat organization and content quality. Notably, the first retreat yielded leadership endorsement and funding for a Quality Improvement pilot to standardize SOGI data collection and clinical staff training. The second retreat provided a platform for updates on focused efforts across the institution and for receiving direction regarding national best practices for SGM care and research. We report the processes and outcomes of institution-wide retreats, which served as a platform for identifying gaps in organizational healthcare practices and research for SGM individuals with cancer. The strategies described herein may be readily scaled at other cancer hospitals seeking to learn and enact system-wide practice changes that support the needs of SGM patients and families.

Age-associated disparity in phagocytic clearance affects the efficacy of cancer nanotherapeutics

Nanomedicines have been approved to treat multiple human diseases. However, clinical adoption of nanoformulated agents is often hindered by concerns about hepatic uptake and clearance, a process that is not fully understood. Here we show that the antitumour efficacy of cancer nanomedicine exhibits an age-associated disparity. Tumour delivery and treatment outcomes are superior in old versus young mice, probably due to an age-related decline in the ability of hepatic phagocytes to take up and remove nanoparticles. Transcriptomic- and protein-level analysis at the single-cell and bulk levels reveals an age-associated decrease in the numbers of hepatic macrophages that express the scavenger receptor MARCO in mice, non-human primates and humans. Therapeutic blockade of MARCO is shown to decrease the phagocytic uptake of nanoparticles and improve the antitumour effect of clinically approved cancer nanotherapeutics in young but not aged mice. Together, these results reveal an age-associated disparity in the phagocytic clearance of nanotherapeutics that affects their antitumour response, thus providing a strong rationale for an age-appropriate approach to cancer nanomedicine.

Adaptive design of mRNA-loaded extracellular vesicles for targeted immunotherapy of cancer

The recent success of mRNA therapeutics against pathogenic infections has increased interest in their use for other human diseases including cancer. However, the precise delivery of the genetic cargo to cells and tissues of interest remains challenging. Here, we show an adaptive strategy that enables the docking of different targeting ligands onto the surface of mRNA-loaded small extracellular vesicles (sEVs). This is achieved by using a microfluidic electroporation approach in which a combination of nano- and milli-second pulses produces large amounts of IFN-γ mRNA-loaded sEVs with CD64 overexpressed on their surface. The CD64 molecule serves as an adaptor to dock targeting ligands, such as anti-CD71 and anti-programmed cell death-ligand 1 (PD-L1) antibodies. The resulting immunogenic sEVs (imsEV) preferentially target glioblastoma cells and generate potent antitumour activities in vivo, including against tumours intrinsically resistant to immunotherapy. Together, these results provide an adaptive approach to engineering mRNA-loaded sEVs with targeting functionality and pave the way for their adoption in cancer immunotherapy applications.

Listeriolysin O Drives Innate and Adaptive Immune Responses to CD47 Immunotherapy

PURPOSE/OBJECTIVE(S)

Radioimmunotherapies that combine radiation with antibodies against the "don't eat me" signal CD47 show increasing promise. One opportunity to synergize RT with anti-CD47 is via the Stimulator of Interferon Genes (STING) pathway which facilitates potent immune responses to cytoplasmic DNA. Anti-CD47 should activate STING by increasing macrophage consumption of tumor DNA. However, tumor contents are destroyed in phagolysosomes. Listeria (L.) monocytogenes escape lysosomes by secreting a pore-forming protein Listeriolysin O (LLO). We recently engineered a protein-antibody conjugate linking anti-CD47 to LLO. Here, we demonstrate that LLO-CD47 enhances macrophage STING signaling, tumor cell phagocytosis, and tumor antigen presentation. At doses compatible with minimal toxicity in mice, LLO-CD47 delays the growth of orthotopic breast tumors. By contrast, anti-CD47 fails to activate STING in macrophages or inhibit tumor growth. We further hypothesize that LLO-CD47 requires innate and adaptive immune cells for antitumor immunity.

MATERIALS/METHODS

Anti-CD47 was conjugated to LLO using a water-soluble SPDP crosslinker and purified by affinity chromatography. Transmission electron microscopy (TEM) was used to visualize the integrity of macrophage phagolysosomes following treatment. C57B6 mouse bone marrow-derived macrophages (BMDMs) were used to study the impact of LLO-CD47 on M2-to-M1 polarization, tumor cell phagocytosis, STING activation, and antigen presentation. CD8+ T cells or tumor-associated macrophages (TAMs) were depleted from tumor-bearing mice using an anti-CD8 antibody or anti-CSF-1R antibody prior to LLO-CD47 treatment.

RESULTS

(1) LLO-CD47 skews BMDMs from M2-to-M1 inflammatory phenotypes and enhances the phagocytosis of E0771 tumor cells. (2) BMDMs visualized by TEM show breaches in phagosome membranes following LLO-CD47, but not anti-CD47, treatment. (3) LLO-CD47 increases levels of phosphorylated STING, IFN, and TNFα relative to cells treated with anti-CD47. (4) LLO-CD47 significantly inhibits the growth of orthotopically implanted E0771 murine breast tumors relative to anti-CD47. (5) The elimination of CD8+ T cells or TAMs abrogates the antitumor effect of LLO-CD47.

CONCLUSION

LLO-CD47 is a de novo protein-antibody conjugate engineered for cGAS-STING pathway activation in innate immune cells. CD8+ T cells and TAMs are required for the antitumor activity LLO-CD47 in orthotopic models of breast cancer. This novel immunotherapy builds on clinical interest in myeloid checkpoint inhibitors and may be studied as a supplemental therapy for patients with metastatic breast cancer.

Dorsal Column Myelopathy Following Intrathecal Chemotherapy for Leukemia

PURPOSE/OBJECTIVE(S)

Intrathecal (IT) methotrexate (Mtx) and/or cytarabine (AraC) improve CNS disease control in patients (pts) with hematologic malignancies. There are increasing number of case reports of irreversible, primarily dorsal column myelopathy in pts treated with IT chemotherapy. By describing the largest case series of myelopathy following IT chemotherapy, we aim to raise awareness about this devastating albeit rare complication.

MATERIALS/METHODS

We retrospectively reviewed 25 pts with leukemia who developed paraplegia following IT chemotherapy between 2/2006 and 9/2021. Clinical/treatment characteristics, response, and toxicity were extracted from the medical records.

RESULTS

Seventeen pts (68%) were male, 16 had B-cell ALL (64%), 4 had AML (16%), 2 had CML (8%), 2 had T-ALL (8%), and 1 had BPDCN (4%). The median age at diagnosis was 38 years (IQR 30-59). All pts required systemic salvage treatment after induction chemotherapy with a median number of 3 regimens received (IQR 2-5.5). In total, the median number of IT treatments was 19 per pt (IQR 14-27). Most pts (84%, n = 21) received single agent IT Mtx alternating with single agent AraC. Fifteen pts (60%) received triple IT therapy with a median of 3 treatments (IQR 0-8). Prior to the onset of myelopathy, 10 pts (40%) received allogeneic SCT and 9 pts (36%) were treated with radiation therapy. Median follow-up from diagnosis was 1.9 yrs (IQR 1.3-4.1). Myelopathy was progressive and irreversible in all pts (n = 25); 84% (n = 21) experienced sensory loss, and all pts had extremity weakness. Symptoms were ascending in 11 pts (44%) and descending in 4 pts (16%). Irreversible bowel/bladder incontinence developed in 12 pts (48%). CSF analysis at the time of symptom onset was negative for leukemia cells in most pts (n = 21, 84%) and showed malignant cells in 4 pts (16%). CSF studies showed elevated protein in 21 pts (84%). Myelin basic protein was elevated in all 13 assessed pts. On T2 weighted spinal MRI, all pts had enhancement of the dorsal columns, including 80% of pts with this dorsal column abnormality reported at the time of the study and 20% of pts (n = 5) with the dorsal enhancement noted retrospectively. Due to concern for occult disease, 20 pts (80%) received additional CNS-directed therapy after symptom onset. Twenty-two pts (88%) died at last follow-up. The time between neurological symptom onset and death was a median 3.5 months (IQR 2.6 and 5). Three pts (12%) are alive with paraplegia at a median of 4.4 years from symptom onset.

CONCLUSION

Dorsal column myelopathy is a rare but devastating condition that can occur after IT chemotherapy in heavily pre-treated leukemia pts. T2 weighted spinal MRI can be helpful in the evaluation of pts that present with unexplained weakness and sensory changes. We recommend delaying additional CNS-directed therapy until work-up to rule out alternative etiologies is complete. Future strategies are desperately needed to address this irreversible treatment complication.

Outcomes and Toxicities in Patients with Diffuse Large B-Cell Lymphoma of the Gastrointestinal Tract

PURPOSE/OBJECTIVE(S)

Diffuse large B-cell lymphoma (DLBCL) involving the gastrointestinal (GI) tract is rare and long-term outcomes are not well defined. Combined modality therapy (CMT) with radiotherapy (RT) in addition to systemic therapy in this setting is not commonly pursued. We aim to characterize outcomes in patients with GI DLBCL treated with systemic therapy, with or without RT.

MATERIALS/METHODS

Patients diagnosed with DLBCL of the GI tract (with or without mesenteric involvement) treated at a single institution from 1988-2022 were retrospectively reviewed on an IRB-approved protocol. Clinical and treatment data were collected including adverse events (AE; acute vs late defined as before or 4 weeks after therapy end). Kaplan-Meier and Cox regression models were used to estimate survival.

RESULTS

Of 207 patients, 62% were male and median age at diagnosis was 63 (IQR 52-73). Gastric involvement was most common (n = 130, 63%), followed by small intestines (n = 48, 23%) and colon/rectum (n = 24, 12%). Most presented with early-stage disease (n = 124, 60%), with a median IPI score of 1. All patients received chemotherapy. Of 182 treated with CHOP/EPOCH, 36 (20%) were treated in the pre-rituximab era while 146 (80%) received rituximab. 66 patients (32%) were treated with RT, 89% as part of first line CMT. 50 cases (76%) received consolidative RT, while 10 (15%) targeted residual gross disease and 4 (6%) targeted distant sites. Median dose and fractionation were 36Gy (IQR 30.6-39.6) in 18 fractions (IQR 17-22). Over half (n = 132, 64%) developed grade 3+ acute chemotherapy AEs, and the most common were anemia (n = 64), febrile neutropenia (n = 40), and neutropenia (n = 20). Grade 3+ late chemotherapy AEs occurred in 14 patients (7%). Acute grade 3+ radiation AEs were uncommon (n = 2, 3%; colitis, emesis). No grade 3+ late radiation AEs were noted. Median follow-up was 46 months (IQR 16-97). 169 (81.6%) had a complete response (CR), with 154 (91%) after first line chemotherapy, 9 (5%) after second line, and 6 (4%) after RT. CR was defined by PET (62%), endoscopy (22%), CT (9%), or other methods (7%). The 5-year progression-free survival for those treated with one line of chemotherapy with or without RT was 95%. Median overall survival (OS) was not reached. Improved OS was associated with early-stage disease (p = 0.003), low IPI (p = 0.001), fewer chemotherapy lines (p<0.001), and CR (p<0.001). OS did not differ by gender, age, immunophenotype, GI site, SUVmax, or RT. Patients with early stage DLBCL treated with RT in the post-rituximab era received fewer chemotherapy cycles compared to those treated without RT (p = 0.02; median of 4 (IQR 3-6) vs 6 cycles (IQR 4-6)), with no OS difference.

CONCLUSION

GI DLBCL patients have favorable outcomes after CMT with minimal late toxicity. CMT with RT to the GI tract is well tolerated with no OS difference compared to chemotherapy alone, and may mitigate risks from additional chemotherapy cycles for selected early-stage patients.

Sexual Orientation and Gender Identity (SOGI) Data Collection: Opportunities to Advance Best Clinical Practices for LGBTQ+ Patients in Radiation Oncology

PURPOSE/OBJECTIVE(S)

A long-standing barrier to progress against health disparities is the lack of data regarding cancer risks, prevalence, treatment, and outcomes for sexual and gender minority (SGM) patients. Sexual orientation and gender identity (SOGI) data are not routinely collected by individual oncologists, cancer centers, or most non-federal hospital systems. Alarmingly high proportions of SGM patients report discrimination in healthcare or avoid routine care due to perceived lack of acceptance in the healthcare system. For these and other reasons, healthcare institutions must adopt practices that promote an inclusive environment for all patients including those self-identified from SGM groups. One strategy to achieve this aim is through SOGI data collection. The purpose of this study was to pilot new procedures and training for SOGI data collection, the aims of this project were to standardize the collection of SOGI data for all new patients referred to the Division of Radiation Oncology; promote clinical staff awareness of SGM health disparities and strategies for fostering an inclusive hospital environment; and to provide SGM patients and caregivers educational resources and support systems tailored to their needs.

MATERIALS/METHODS

We designed a Quality Improvement program for collecting SOGI data, which was approved by our institution's QIAB. Patient access specialists (PAS) were trained to collect SOGI data from newly registered patients and enter the data into the electronic health record. Radiation Oncology staff completed surveys before and after SOGI training to estimate its impact on the provision of patient care. A Fisher's exact test was utilized to evaluate associations between training and provider-reported outcomes.

RESULTS

Within a 3-week period starting in January 2023, two 1-hour interactive training sessions were offered to twenty-five PAS. Three 1-hour training sessions were offered to twenty-seven Radiation Oncology clinical staff. (1) Confidence for incorporating SOGI classifiers around patients improved from before training (52%, 13/25) to after training (100%, 17/17) among medical providers surveyed (odds ratio (OR) 32, 95% confidence interval (CI) 0.70-1493, p = 0.005). Use of SOGI data in clinical decision making increased from before training (9/25, 36%) to after training (100%, 17/17) among medical providers (OR 60.79, 95% CI 3.271-1130, p<0.0001). (2) A clinical pathway for SGM patients was developed to facilitate referral to our institution's SGM patient support group and distribution of patient education materials focused on sexual health.

CONCLUSION

Establishing standardized SOGI data collection can facilitate the provision of tailored resources and care that meets the needs of patients and staff in a large comprehensive cancer center. Specialized training for staff developed through this initiative helps foster an inclusive and welcoming environment that promotes the integration, visibility, and advancement of SGM cancer care at our institution.

Ultra Low-Dose Radiation for Extranodal Marginal Zone Lymphoma of the Lung

PURPOSE/OBJECTIVE(S)

Definitive radiation treatment (RT) for extranodal marginal zone lymphoma (ENMZL) of mucosal associated lymphoid tissue historically involves treatment to 24-30 Gy. There is increasing data supporting the use of ultra-low dose RT as part of a response-adapted approach in the treatment of orbital and gastric ENMZL. With this approach, patients receive initial treatment with 4 Gy, and additional RT is considered for those with persistent or locally progressive disease. However limited data to date assesses the efficacy of 4 Gy in the management of ENMZL of the lung.

MATERIALS/METHODS

We performed an IRB-approved retrospective review of 17 patients with ENMZL of the lung treated with 4 Gy between 7/2015 and 12/2022 with response assessed after RT. Clinical/treatment characteristics, response, and toxicity were extracted from medical records. Statistics were performed using Mann-Whitney U and Fisher's Exact Test.

RESULTS

Eight patients (47%) were female, 15 (88%) white, and 1 (6%) Hispanic. Median age at RT was 66 (interquartile range (IQR) 59-77). All had disease limited to the lung at diagnosis and 15 had stage IE disease. Four patients (24%) were diagnosed incidentally on screening/surveillance imaging in the absence of symptoms. Sixteen patients received 4 Gy in 2 fractions, while one patient received a single fraction of 4 Gy. Median SUVmax prior to RT was 4.5 (IQR 3.2-7.2). Median planning target volume (PTV) was 74 cc (IQR 47-130cc). Six patients (35%) had respiratory symptoms prior to RT, which improved or resolved in 3 (50%). A larger PTV was associated with improvement in symptoms following RT with a median PTV of 266 cc (IQR 171-402) in those who experienced improvement vs. 64 cc (IQR 42-100) in those who did not (p = 0.032). One patient experienced toxicity following RT with pleuritic chest pain, which resolved with corticosteroids. At a median follow-up of 15 months following RT (IQR 7-43 months), the overall response rate (ORR) was 100% (CR, n = 15; PR, n = 2). Fourteen patients had follow-up PET/CT, of whom 13 had a complete metabolic response (CMR) at a median of 3 months following RT (IQR 3-5 months). Two additional patients had a complete response (CR) on CT while one had a partial response on CT. Achieving a CR was not associated with SUV prior to RT (p = 0.50) or PTV size (p = 0.62). In patients with stage IE disease, the ORR rate was 100% and there have been no distant failures to date. Fifteen of 17 patients were alive at last follow-up; two passed away of unrelated causes (one from Alzheimer's disease and one from recurrent squamous cell carcinoma).

CONCLUSION

Ultra-low dose radiation of 4 Gy is associated with excellent local control in the management of ENMZL of the lung and is very well tolerated. Four Gy was effective for local control and symptom palliation even for larger tumors and is an effective initial therapy as part of a response-adapted approach even in limited stage patients.

Multiscale reorganization of the genome following DNA damage facilitates chromosome translocations via nuclear actin polymerization

Nuclear actin-based movements have been shown to orchestrate clustering of DNA double-strand breaks (DSBs) into homology-directed repair domains. Here we describe multiscale three-dimensional genome reorganization following DNA damage and analyze the contribution of the nuclear WASP-ARP2/3-actin pathway toward chromatin topology alterations and pathologic repair. Hi-C analysis reveals genome-wide, DNA damage-induced chromatin compartment flips facilitated by ARP2/3 that enrich for open, A compartments. Damage promotes interactions between DSBs, which in turn facilitate aberrant, actin-dependent intra- and inter-chromosomal rearrangements. Our work establishes that clustering of resected DSBs into repair domains by nuclear actin assembly is coordinated with multiscale alterations in genome architecture that enable homology-directed repair while also increasing nonhomologous end-joining-dependent translocation frequency.

Immunological conversion of solid tumours using a bispecific nanobioconjugate for cancer immunotherapy

Solid tumours display a limited response to immunotherapies. By contrast, haematological malignancies exhibit significantly higher response rates to immunotherapies as compared with solid tumours. Among several microenvironmental and biological disparities, the differential expression of unique immune regulatory molecules contributes significantly to the interaction of blood cancer cells with immune cells. The self-ligand receptor of the signalling lymphocytic activation molecule family member 7 (SLAMF7), a molecule that is critical in promoting the body's innate immune cells to detect and engulf cancer cells, is expressed nearly exclusively on the cell surface of haematologic tumours, but not on solid ones. Here we show that a bispecific nanobioconjugate that enables the decoration of SLAMF7 on the surface of solid tumours induces robust phagocytosis and activates the phagocyte cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) pathway, sensitizing the tumours to immune checkpoint blockade. Our findings support an immunological conversion strategy that uses nano-adjuvants to improve the effectiveness of immunotherapies for solid tumours.

Genome-encoded cytoplasmic double-stranded RNAs, found in C9ORF72 ALS-FTD brain, propagate neuronal loss

Triggers of innate immune signaling in the CNS of patients with amyotrophic lateral sclerosis and frontotemporal degeneration (ALS/FTD) remain elusive. We report the presence of cytoplasmic double-stranded RNA (cdsRNA), an established trigger of innate immunity, in ALS-FTD brains carrying C9ORF72 intronic hexanucleotide expansions that included genomically encoded expansions of the G₄C₂ repeat sequences. The presence of cdsRNA in human brains was coincident with cytoplasmic TAR DNA binding protein 43 (TDP-43) inclusions, a pathologic hallmark of ALS/FTD. Introducing cdsRNA into cultured human neural cells induced type I interferon (IFN-I) signaling and death that was rescued by FDA-approved JAK inhibitors. In mice, genomically encoded dsRNAs expressed exclusively in a neuronal class induced IFN-I and death in connected neurons non-cell-autonomously. Our findings establish that genomically encoded cdsRNAs trigger sterile, viral-mimetic IFN-I induction and propagated death within neural circuits and may drive neuroinflammation and neurodegeneration in patients with ALS/FTD.

Loss of interneuron LTD and attenuated pyramidal cell LTP in Trpv1 and Trpv3 KO mice

TRPV (transient receptor potential, vanilloid) channels are a family of nonselective cation channels that are activated by a wide variety of chemical and physical stimuli. TRPV1 channels are highly expressed in sensory neurons in the peripheral nervous system. However, a number of studies have also reported TRPV channels in the brain, though their functions are less well understood. In the hippocampus, the TRPV1 channel is a novel mediator of long-term depression (LTD) at excitatory synapses on interneurons. Here we tested the role of other TRPV channels in hippocampal synaptic plasticity, using hippocampal slices from Trpv1, Trpv3 and Trpv4 knockout (KO) mice. LTD at excitatory synapses on s. radiatum hippocampal interneurons was attenuated in slices from Trpv3 KO mice (as well as in Trpv1 KO mice as previously reported), but not in slices from Trpv4 KO mice. A previous study found that in hippocampal area CA1, slices from Trpv1 KO mice have reduced tetanus-induced long-term potentiation (LTP) following high-frequency stimulation; here we confirmed this and found a similar reduction in Trpv3 KO mice. We hypothesized that the loss of LTD at the excitatory synapses on local inhibitory interneurons caused the attenuated LTP in the mutants. Consistent with this idea, blocking GABAergic inhibition rescued LTP in slices from Trpv1 KO and Trpv3 KO mice. Our findings suggest a novel role for TRPV3 channels in synaptic plasticity and provide a possible mechanism by which TRPV1 and TRPV3 channels modulate hippocampal output.

Site-specific effects of PECAM-1 on atherosclerosis in LDL receptor-deficient mice

OBJECTIVE

Atherosclerosis is a vascular disease that involves lesion formation at sites of disturbed flow under the influence of genetic and environmental factors. Endothelial expression of adhesion molecules that enable infiltration of immune cells is important for lesion development. Platelet/endothelial cell adhesion molecule-1 (PECAM-1; CD31) is an adhesion and signaling receptor expressed by many cells involved in atherosclerotic lesion development. PECAM-1 transduces signals required for proinflammatory adhesion molecule expression at atherosusceptible sites; thus, it is predicted to be proatherosclerotic. PECAM-1 also inhibits inflammatory responses, on which basis it is predicted to be atheroprotective.

METHODS AND RESULTS

We evaluated herein the effect of PECAM-1 deficiency on development of atherosclerosis in LDL receptor-deficient mice. We found that PECAM-1 has both proatherosclerotic and atheroprotective effects, but that the former dominate in the inner curvature of the aortic arch whereas the latter dominate in the aortic sinus, branching arteries, and descending aorta. Endothelial cell expression of PECAM-1 was sufficient for its atheroprotective effects in the aortic sinus but not in the descending aorta, where the atheroprotective effects of PECAM-1 also required its expression on bone marrow-derived cells.

CONCLUSIONS

We conclude that PECAM-1 influences initiation and progression of atherosclerosis both positively and negatively, and that it does so in a site-specific manner.