The TEMPI Syndrome: A Monoclonal Gammopathy of Clinical Significance Driving Erythropoietin Production

BACKGROUND. The TEMPI syndrome is a rare monoclonal gammopathy of clinical significance (MGCS) that we discovered in 2011. Patients with the TEMPI syndrome display five hallmark features: (1) Telangiectasias (abnormal blood vessels near the skin's surface), (2) elevated serum Erythropoietin (EPO) levels and erythrocytosis (an excessive increase in red blood cells), (3) Monoclonal gammopathy (an expanded antibody clone), (4) Perinephric fluid collections, and (5) Intrapulmonary shunting (where blood bypasses the lungs without being oxygenated). To date, we have identified 41 patients world-wide.

The elevated serum EPO is one of the most striking features, with EPO levels often exceeding 500‑times the upper limit of normal. This suggests a severe dysregulation of the hypoxia sensing pathway and of EPO production. These very high EPO levels lead to uncontrolled red blood cell production such that patients present with marked erythrocytosis. Patients are commonly misdiagnosed with polycythemia vera.

Plasma cell directed therapies (e.g., bortezomib, lenalidomide, daratumumab) have been used to eradicate the TEMPI MGUS in several patients. Remarkably, elimination of the MGUS leads to complete resolution of the other TEMPI syndrome symptoms, implicating the monoclonal antibody as pathologic driver of the disease.

HYPOTHESIS. Based on the patient experience, we hypothesize that the TEMPI syndrome is an acquired and reversible disease, driven by the auto‑reactive monoclonal gammopathy (MGCS). It stands to reason that the TEMPI syndrome may have a remote pathogenic trigger (e.g., a virus, bacteria, fungi), and that the resulting immune response has some degree of molecular mimicry between the antibody epitope on the pathogen and a partially cross-reactive human membrane protein. We suspect that the antibody has a low affinity to the human target given the very high serum concentration of monoclonal antibody required to drive the other features of the TEMPI syndrome such as the uncontrolled EPO production.

EXPERIMENTS. Bone marrow aspirate samples were collected from 8 patients with the TEMPI syndrome. Plasma cells were isolated, RNA purified, and long read sequencing performed to identify the exact heavy and light chain sequence of the monoclonal antibody (mAb). These sequences were cloned into expression vectors, permitting the in vitro production of eight unique, pure, recombinant, TEMPI patient mAbs.

RESULTS. TEMPI patient mAbs were injected into wild-type C57Bl/6 mice to achieve the same serum monoclonal antibody concentration as seen in patients. Remarkably, the TEMPI mAbs increased the serum EPO concentration as well as increasing the hemoglobin and hematocrit.

Three TEMPI mAbs were used for flow cytometric screening of a membrane proteome array of ~6000 human membrane proteins, generating a candidate list of potential TEMPI auto‑antigens.

Ongoing experiments are underway to confirm the antibody target(s) of the TEMPI syndrome monoclonal antibody(s).

DISCUSSION. After more than a decade of slow insights into this ultra-rare disease, we are finally poised to identify the host antigen target of the TEMPI patient monoclonal antibodies. If successful, this will reveal a completely novel antibody-antigen interaction capable of driving hypoxia independent erythropoietin production. Beyond the fascinating new biology, this may also be the first step in developing therapeutics for those tens of millions of patients who suffer from anemia due to low erythropoietin production.

The TEMPI syndrome is also a model of other MGCS, where identification of the antibody target may shed light on disease pathogenesis.