In the 2026 FDA new drug review cycle, some candidate drugs target treatment gaps-conditions for which there are no approved specialized therapies at the U.S. level, and where current management relies primarily on supportive care, transplantation, invasive procedures, or high-toxicity rescue options.
The most representative areas within this category of unmet need include:
Epstein-Barr virus (EBV)-positive post-transplant lymphoproliferative disorder (PTLD)
Chronic hepatitis D (HDV)
Severe leukocyte adhesion deficiency type I (LAD-I)
Glycogen storage disease type Ia (GSDIa)
Autoimmune pulmonary alveolar proteinosis (aPAP)
Menkes disease, transitioning from no approved therapy to standardized treatment
01 EBV-Positive Post-Transplant Lymphoproliferative Disorder (PTLD)
Drug: Ebvallo
Modality: Allogeneic, EBV-specific T-cell immunotherapy
Sponsor: Pierre Fabre
Indication: EBV-positive PTLD in adults and children ≥2 years old; (per filing) patients who have received at least one prior line of therapy, including anti-CD20-based treatment.
EBV-positive PTLD occurs during the post-transplant immunosuppressive phase. It is driven by EBV-induced abnormal B-cell proliferation, with rapid clinical progression. Symptoms are non-specific: persistent/recurrent fever, night sweats, weight loss; lymphadenopathy or mass formation; hepatosplenomegaly; organ-specific symptoms (e.g., abdominal pain/diarrhea/bleeding in the gastrointestinal tract, cough/dyspnea in the lungs, headache/altered consciousness/focal neurological deficits in the central nervous system); hematological abnormalities (anemia, thrombocytopenia) and elevated lactate dehydrogenase.
Current management first reduces immunosuppression to restore partial immune function, but this increases the risk of transplant rejection. If disease remains uncontrolled, rituximab (anti-CD20) is used to clear B-cell clones. Chemotherapy follows for non-responders or rapidly progressing cases. To date, the U.S. has no approved therapy targeting the disease's etiology; management relies on risk-benefit tradeoffs, experience-based care, and high toxicity risks (especially in immunocompromised post-transplant patients). Relapsed/refractory patients lack standardized treatments, with outcomes dependent on center expertise.
Ebvallo directly targets the EBV-driven etiology. As an allogeneic EBV-specific T-cell immunotherapy, it restores EBV-directed cellular immunity to precisely control infected cells under immunosuppression. Approved in the EU for relapsed/refractory EBV-positive PTLD in adults and children ≥2 years old, it provides a regulatory-endorsed clinical pathway.
If approved in the U.S., benefits include:
A targeted etiology-based option for relapsed/refractory patients, reducing reliance on high-toxicity chemotherapy.
Standardized care across transplant centers, minimizing variability in outcomes.
Market-wise, the small patient base is concentrated in transplant/hematology-oncology centers. Reimbursement focuses on life-saving value, scarcity, and cost offsets (hospitalization/complications). Commercial success depends on access, center coverage, and real-world evidence supporting clinical consensus.
02 Chronic Hepatitis D (HDV)
Drug: Bulevirtide
Modality: Peptide
Sponsor: Gilead
Indication: Chronic HDV infection in adults with compensated liver disease.
Chronic HDV is caused by the hepatitis D virus, which requires HBV envelope proteins to infect and spread-so patients usually have chronic HBV co-infection. Co-infection accelerates fibrosis, increases cirrhosis and liver-related death risk, making it the most severe form of chronic viral hepatitis per WHO. It progresses faster, with higher rates of early cirrhosis, decompensation, and hepatocellular carcinoma.
Diagnostic gaps persist: limited HDV testing, poor access to standardized HDV RNA quantification, leading to missed diagnoses and delayed care. Treatment options in the U.S. are scarce: pegylated interferon is the mainstay, but response rates are low, durability is poor, relapse is common post-treatment, and tolerability limits adherence. Liver transplantation is an option for end-stage disease but faces resource constraints, long wait times, and high perioperative/complication burdens.
Bulevirtide inhibits HBV/HDV entry into hepatocytes by targeting NTCP (sodium taurocholate cotransporting polypeptide), blocking viral uptake. Approved in the EU as Hepcludex (transitioned from conditional to standard marketing authorization), its mechanism is validated by regulators.
If approved in the U.S., benefits include:
Shifting from ineffective, poorly tolerated interferon to a targeted antiviral strategy for more predictable long-term management.
Market-wise, HDV patients are few but burden-heavy. Reimbursement discussions focus on avoiding cirrhosis complications, delaying decompensation, reducing transplantation needs, and lowering hospitalization costs. Success depends on improving screening/diagnosis and specialist pathways-not just prescription substitution.
03 Severe Leukocyte Adhesion Deficiency Type I (LAD-I)
Drug: Kresladi
Modality: Autologous lentiviral gene therapy
Sponsor: Rocket Pharmaceuticals
Indication: Severe LAD-I.
Severe LAD-I is a congenital immunodeficiency caused by ITGB2 mutations, resulting in defective CD18 function-impairing leukocyte adhesion and transendothelial migration. Infants develop recurrent bacterial infections (skin, mucosa, respiratory tract) with poor inflammation, minimal pus, and delayed wound healing. Clues include delayed umbilical cord separation and persistent neutrophilia. Without curative intervention, early mortality is high.
Current care uses antibiotics/supportive measures to manage acute events. Hematopoietic stem cell transplantation (HSCT) is the only disease-modifying option, aiming to reconstitute functional immune cells.
Unmet needs: HSCT depends on donor availability/timing, carries toxicity (graft-versus-host disease), and requires long-term center-based management. No LAD-I-specific therapy is approved in the U.S.; care relies on antibiotics and supportive care.
Kresladi uses autologous lentiviral gene therapy: collect the patient's hematopoietic stem cells, insert a functional gene via lentivirus, and reinfuse to reconstitute immune cells with normal adhesion/migration.
If approved, benefits include:
A curative, donor-independent option (vs. HSCT), reducing infection/ hospitalization risks long-term.
Market-wise, this fits the ultra-rare disease model: small patient numbers, high per-case value, reimbursement based on lifetime cost offsets. Success depends on manufacturing speed, center certification, long-term follow-up, and early diagnosis/referral efficiency.
04 Glycogen Storage Disease Type Ia (GSDIa)
Drug: Pariglasgene brecaparvovec
Modality: Gene therapy
Sponsor: Ultragenyx
Indication: GSDIa.
GSDIa is an autosomal recessive metabolic disorder caused by impaired glucose-6-phosphatase activity, preventing fasting glucose production and leading to glycogen/lipid accumulation in the liver/kidneys. Symptoms start in infancy: recurrent fasting hypoglycemia (with seizure/drowsiness risk), hepatomegaly, growth failure, lactic acidosis, hyperlipidemia, and hyperuricemia.
Management requires strict fasting avoidance-frequent meals/uncooked starch to maintain blood sugar, often with overnight infusions. This extends survival and reduces acute hypoglycemia but does not address the root cause. Long-term complications (liver adenomas, kidney damage) persist, burdening quality of life, adherence, and monitoring. Liver transplantation is an option for severe liver disease but does not reverse kidney damage; combined liver-kidney transplantation is limited by donor resources and risks.
Pariglasgene brecaparvovec is an AAV8 vector-based liver-targeted gene therapy: a single IV dose delivers a key glucose homeostasis gene to restore enzyme activity in hepatocytes, reducing reliance on continuous glucose supplementation.
If approved, benefits include:
Reduced dependence on glucose supplementation, lower nocturnal management stress, and fewer acute hypoglycemic events.
Potential long-term reduction in complications (e.g., liver adenomas).
Market-wise, reimbursement focuses on offsetting long-term compensation costs, complication treatments, and acute event risks. Success depends on diagnosis rates, specialist referrals, center capacity, and real-world evidence of sustained efficacy.
05 Autoimmune Pulmonary Alveolar Proteinosis (aPAP)
Drug: Molbreevi
Modality: Protein biologic
Sponsor: Savara
Indication: aPAP.
aPAP results from impaired alveolar macrophage clearance of surfactant, leading to surfactant accumulation and reduced gas exchange. Symptoms include progressive exertional dyspnea, fatigue, cough, and hypoxemia; lung function shows reduced diffusion capacity, and imaging reveals alveolar opacities.
Whole-lung lavage (WLL)-anesthesia-dependent, invasive procedure to wash out surfactant-is the mainstay, providing rapid relief but requiring specialist centers. Recurrence is common, necessitating repeat WLL. No approved drugs exist, so care alternates between invasive procedures and observation. Unmet need: a sustainable, outpatient-friendly long-term therapy.
Molbreevi is an inhaled recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) that restores alveolar macrophage function to reduce surfactant accumulation upstream.
If approved, benefits include:
Reduced reliance on invasive WLL; maintenance therapy feasible in outpatient settings.
Long-term follow-up focused on lung function and quality of life.
Market-wise, this is a niche rare disease. Commercial success depends on respiratory center coverage, diagnostic standardization, and payer recognition of reduced WLL/hospitalization costs. It could advance drug-based management of rare lung diseases.
06 Menkes Disease: From No Therapy to Standardized Care
Drug: Zycubo
Sponsor: Sentynl Therapeutics
Indication: Pediatric Menkes disease
Approval Date: January 12, 2026
Menkes disease is a pediatric rare genetic disorder of copper transport, starting in infancy with rapid progression. Symptoms involve neurological (developmental delay, hypotonia, seizures, lethargy) and connective tissue (sparse/brittle light-colored hair, fragile skin/vessels, hypothermia) features. Copper-dependent enzyme deficiencies affect multiple organs; prognosis is poor without intervention.
Zycubo's approval provides the first regulatory-approved, standardized therapy for Menkes disease. For clinicians, this shifts care from empirical management to consistent, time-sensitive treatment initiation and follow-up. For payers, it establishes access rules (indications, dosing, monitoring) and center requirements. For families, it increases certainty and access-reducing delays from fragmented care.
(Note: This article is for informational purposes only. Views do not represent any position and are not treatment recommendations. For medical advice, consult a qualified healthcare provider.)
