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Clinical Study Report (OBX319-301)

Document ID: CSR-301
Version: 1.0
Change History: 1.0 — Initial issue.
Standard(s): ICH E3

Clinical Study Report — OBX319-301

This clinical study report describes OBX319-301, the confirmatory Phase 3 efficacy and safety study of OBX-319 in adults with moderate-to-severe active Systemic Lupus Erythematosus (SLE), sponsored by Virtual Biopharma Inc. OBX-319 is a humanized IgG1 bispecific monoclonal antibody that simultaneously engages CD19 and CD20 on the B-cell lineage and is administered subcutaneously. The molecule is produced by recombinant expression in a Chinese Hamster Ovary (CHO) cell line and purified using a platform downstream process (Protein A affinity capture followed by orthogonal polishing chromatography and dedicated viral-clearance steps), and is developed for marketing as a biological product under a Biologics License Application (21 CFR Part 601), with quality, comparability, and specification aspects governed by ICH Q5A(R2), Q5C, and Q6B. By co-targeting CD20 (expressed from the pre-B stage through mature and memory B cells) and CD19 (expressed earlier in the lineage and persisting on plasmablasts and a subset of short-lived plasma cells), OBX-319 is intended to produce deeper and broader depletion of the pathogenic B-cell pool than single-antigen anti-CD20 approaches, through the intact human IgG1 Fc via ADCC, ADCP, and CDC. The report is organised to ICH E3; sections are numbered per the E3 template, and cross-referenced modules (Module 2.7.3 Summary of Clinical Efficacy, Module 2.7.4 Summary of Clinical Safety, and the clinical pharmacology reports) provide the integrated context.

9 Investigational Plan

OBX319-301 was a randomized, double-blind, placebo-controlled study in Systemic Lupus Erythematosus (moderate-to-severe active) (N randomized 480). Primary endpoint: SRI-4 response at Week 52 (operationalised as low disease activity, SLEDAI-2K <= 4).

9.1 Overall study design and plan

OBX319-301 was a multicentre, randomized, double-blind, placebo-controlled, parallel-group study with 1:1:1 allocation to OBX-319 High-dose, OBX-319 Low-dose, or matched subcutaneous placebo, each added to background standard of care, over a 52-week double-blind treatment period. Approximately 900 subjects were screened to randomize 480 (OBX-319 High 162, OBX-319 Low 158, Placebo 160). Randomization was managed centrally through an interactive response technology (IRT) system and was stratified to balance baseline disease activity (SLEDAI-2K category) and background standard-of-care therapy across arms. Study assessments were performed at the pre-specified visits at Weeks 0, 4, 12, 24, 36, and 52, with the primary endpoint evaluated at Week 52. Masking was maintained by supplying OBX-319 and placebo as visually identical subcutaneous presentations administered on an identical schedule, preserving the double blind for subjects, investigators, and sponsor personnel for the duration of the randomized period.

9.2 Rationale for study design and choice of control

A placebo-controlled superiority design on a background of standard of care is the established approach for confirmatory efficacy in active SLE, because it isolates the contribution of the investigational agent while ensuring that no subject is deprived of accepted therapy (glucocorticoids, antimalarials, and/or conventional immunosuppressants). Two active dose levels were studied to characterise the dose-response relationship and to support dose selection. The 52-week duration was chosen to capture the induction and consolidation of B-cell-depletion–driven disease control and to allow durable disease-activity endpoints and organ-domain responses to mature. The design and analytical framework are consistent with ICH E6(R3) and ICH E9(R1).

9.3 Selection of study population

Eligible subjects were adults with a clinical diagnosis of SLE meeting accepted classification criteria and with moderate-to-severe active disease at entry, reflected in a mean baseline SLEDAI-2K of approximately 11 and seropositivity typical of the target population. Enrolment required active disease despite background therapy, and subjects were maintained on stable background standard of care during the double-blind period within protocol-defined limits. Exclusion criteria addressed active or latent serious infection, severe organ-threatening manifestations requiring immediate alternative therapy, and other conditions that would confound the assessment of B-cell-directed therapy or place subjects at undue risk, consistent with the known class risks of B-cell depletion.

9.4 Treatments, administration, and blinding

OBX-319 was administered subcutaneously at two dose levels (High and Low); matched subcutaneous placebo was administered on the same schedule. Because OBX-319 acts through direct depletion of CD19/CD20-bearing B cells, its disposition is governed by target-mediated drug disposition (TMDD), and the dosing regimen was designed to achieve and maintain target saturation and sustained peripheral B-cell depletion across the interval. All subjects continued background standard of care. Prohibited and rescue medications, and the thresholds that constituted an intercurrent event for the efficacy estimand, were pre-specified.

9.5 Efficacy, pharmacodynamic, and safety variables

The pre-specified primary efficacy variable was SRI-4 response at Week 52, operationalised as low disease activity (SLEDAI-2K <= 4). SLEDAI-2K is a weighted composite of 24 descriptors across nine organ systems (theoretical range 0–105); SRI-4 requires a ≥4-point reduction from baseline in SLEDAI-2K, no clinically meaningful organ-domain worsening (no new BILAG A and no more than one new BILAG B), and no worsening of the Physician's Global Assessment, without treatment discontinuation or restricted/rescue medication beyond thresholds. Secondary and supportive variables included the continuous LS-mean change from baseline in SLEDAI-2K, BILAG-based organ-domain response, disease flare, and glucocorticoid dose reduction. Mechanistic pharmacodynamic and serological variables — circulating CD19+ B-cell counts, anti-dsDNA titres, and complement C3/C4 — were collected to confirm target engagement. As an exogenous therapeutic protein, OBX-319 carries an inherent potential for immunogenicity; binding and neutralizing anti-drug antibodies (ADA) were monitored throughout using a tiered validated assay strategy, given the potential for ADA to affect exposure. Safety variables comprised adverse events, deaths, serious adverse events, discontinuations, injection-site and hypersensitivity reactions, and laboratory monitoring relevant to B-cell depletion (immunoglobulins, lymphocyte/B-cell counts, neutrophils).

9.7 Statistical methods and sample size

The primary continuous analysis of SLEDAI-2K change from baseline at Week 52 used ANCOVA (change from baseline ~ treatment + baseline), yielding least-squares mean changes by arm and placebo-adjusted differences with two-sided 95% confidence intervals; the binary low-disease-activity (SLEDAI-2K <= 4) endpoint was analysed by responder analysis with risk difference versus placebo and a normal-approximation 95% CI. Type-I error was controlled at α = 0.05 (two-sided) across the primary and key secondary comparisons through a pre-specified hierarchical (fixed-sequence) testing procedure. The randomization of 480 subjects provided approximately 90% power to detect the anticipated treatment difference at α = 0.05. Efficacy was analysed primarily on the Full Analysis Set with supportive per-protocol analyses; the binary responder endpoint used the pre-specified responder analysis set with non-responder handling of intercurrent events.

9.8 Study oversight and quality assurance

The study was conducted in accordance with ICH E6(R3) Good Clinical Practice and applicable regulatory requirements, under approved protocol and informed consent. An independent Data Safety Monitoring Board (DSMB) reviewed unblinded safety data at pre-specified intervals, with particular attention to the identified class risks of serious and opportunistic infection and hypogammaglobulinaemia. The nonclinical program supporting the study was conducted in cynomolgus monkey as the sole pharmacologically relevant toxicology species (there is no rodent cross-reactivity for the CD19/CD20 targets), consistent with ICH S6(R1); as expected for a monoclonal antibody, genotoxicity, carcinogenicity, and dedicated hERG/thorough-QT studies were not warranted and were not conducted.

11 Efficacy Evaluation

Arm	N	LS-mean Δ SLEDAI-2K @ Wk 52 (points)	Diff vs placebo (95% CI)	p
OBX-319 High	162	-6.37	-2.91 (-3.12, -2.69)	0.0000
OBX-319 Low	158	-5.62	-2.17 (-2.38, -1.95)	0.0000
Placebo	160	-3.46	— (reference)	—

Responder analysis — Low disease activity (SLEDAI-2K <= 4)

Arm	N	Responders, n/N	Rate	Risk diff vs placebo (95% CI, %)	p
OBX-319 High	145	76/145	52.4%	46.4% (37.4, 55.4)	0.0000
OBX-319 Low	145	49/145	33.8%	27.8% (19.2, 36.4)	0.0000
Placebo	150	9/150	6.0%	— (reference)	—

11.1 Data sets analysed

The primary continuous analysis of SLEDAI-2K change was performed on the Full Analysis Set (N = 480), comprising all randomized subjects analysed according to randomized treatment (OBX-319 High 162, OBX-319 Low 158, Placebo 160). The binary low-disease-activity (SLEDAI-2K <= 4) responder endpoint was evaluated on the pre-specified responder analysis set, with intercurrent events (discontinuation of randomized treatment, use of prohibited/rescue medication, or a missing Week 52 assessment) handled by non-responder imputation; the corresponding per-arm denominators (145, 145, 150) are shown in the responder table. Supportive per-protocol analyses were consistent with the Full Analysis Set.

11.2 Demographic and baseline characteristics

Treatment groups were well balanced at baseline with respect to demographics, SLE duration, background standard-of-care therapy, and serological status, consistent with successful stratified randomization. The population had active disease at entry, with a mean baseline SLEDAI-2K of approximately 11, and the majority were seropositive (anti-dsDNA and/or low complement), consistent with the moderate-to-severe active target indication.

11.3 Treatment compliance

Administration of subcutaneous study drug and placebo was documented at each dosing visit, and background standard of care was maintained within protocol limits. Overall exposure and adherence were high and comparable across arms, supporting the interpretability of the Week 52 endpoints.

11.4 Analysis of efficacy and dose-response

Both OBX-319 regimens produced statistically significant and clinically meaningful improvements over placebo on both the continuous and responder formulations of the primary endpoint, with a consistent dose-ordered relationship (High-dose > Low-dose > placebo). On the continuous analysis, the LS-mean reduction in SLEDAI-2K at Week 52 was -6.37 points for High-dose and -5.62 points for Low-dose versus -3.46 for placebo, corresponding to placebo-adjusted treatment differences of -2.91 (95% CI -3.12, -2.69) and -2.17 (95% CI -2.38, -1.95), respectively. On the responder analysis, 52.4% (76/145) of High-dose and 33.8% (49/145) of Low-dose subjects achieved low disease activity (SLEDAI-2K <= 4) at Week 52, versus 6.0% (9/150) on placebo, yielding placebo-adjusted risk differences of 46.4 percentage points (95% CI 37.4, 55.4) for High-dose and 27.8 percentage points (95% CI 19.2, 36.4) for Low-dose. The magnitude of these differences is large relative to the modest placebo response expected in an active-disease SLE population maintained on background therapy, and the ordering of both point estimates and confidence intervals across dose levels supports the selected High-dose regimen while confirming activity at the Low dose.

11.5 Pharmacodynamic and serological corroboration

The efficacy findings are mechanistically corroborated by concordant pharmacodynamic and serological data providing direct evidence of target engagement by this CD19 × CD20 bispecific antibody. On the active arms, OBX-319 produced near-complete depletion of circulating CD19+ B cells (from approximately 210 to approximately 7 cells/µL), whereas B-cell counts were essentially unchanged in the placebo arm. Depletion of the autoreactive B-cell compartment was accompanied by serological normalization: anti-dsDNA titres fell and complement components C3 and C4 normalised in association with clinical response. The temporal and directional coherence of profound peripheral B-cell depletion, declining anti-dsDNA, and recovering complement — each a recognized correlate of SLE disease activity — provides biologically plausible, target-engagement–linked support for the primary and continuous efficacy results.

11.6 Statistical/analytical issues and sensitivity analyses

Type-I error was controlled by the pre-specified hierarchical testing procedure at α = 0.05 (two-sided), so that formal significance at each step was contingent on success at the preceding step, preserving the family-wise error rate across the dose comparisons and their continuous and responder framings. Robustness of the primary conclusions to missing-data assumptions was examined through pre-specified sensitivity analyses (including tipping-point and reference-based multiple-imputation approaches for the continuous endpoint and per-protocol re-analysis); these were consistent with the primary analysis and did not alter the interpretation.

11.7 Secondary, subgroup, and immunogenicity considerations

Pre-specified secondary and supportive analyses (organ-domain/BILAG response, disease flare, and glucocorticoid dose reduction) were directionally consistent with the primary result and reinforced the dose-ordered benefit. Efficacy was consistent across the clinically relevant baseline subgroups examined (including baseline disease-activity category and background standard-of-care therapy), with no subgroup showing a qualitative reversal of effect. Anti-drug antibodies (binding and neutralizing) were monitored throughout; the presence of ADA did not attenuate the depletion pharmacodynamics or the disease-activity response in a manner that altered the efficacy conclusions. Consistent with TMDD, the near-complete and durable peripheral B-cell depletion observed on the active arms indicates target saturation over the dosing interval and supports the durability of the Week 52 effect.

12 Safety Evaluation

Arm	N	≥1 TEAE	SAE	Deaths	Discontinued
OBX-319 High	162	78	2	1	17
OBX-319 Low	158	74	1	0	13
Placebo	160	78	1	0	10

Most frequent adverse events (subjects, by arm)

Preferred term	OBX-319 High	OBX-319 Low	Placebo
Upper respiratory tract infection	25	18	13
Urinary tract infection	16	14	14
Nasopharyngitis	11	14	16
Headache	11	11	16
Lupus nephritis flare	4	8	16
Injection site reaction	14	7	6

12.1 Extent of exposure

All 480 randomized subjects who received at least one dose were included in the safety evaluation, analysed by treatment actually received, over the 52-week double-blind period (OBX-319 High 162, OBX-319 Low 158, Placebo 160). Exposure was comparable across arms and consistent with the planned subcutaneous dosing schedule.

12.2 Adverse events

The overall adverse-event burden was similar across arms (≥1 TEAE in 78, 74, and 78 subjects for High, Low, and placebo, respectively), and the event profile was consistent with the B-cell-depleting bispecific monoclonal antibody class. The most frequently reported events were infections of the upper respiratory and urinary tracts and nasopharyngitis, in keeping with the expected consequence of B-cell depletion; upper respiratory tract infection showed a dose-ordered frequency (25 High, 18 Low, 13 placebo). Injection-site reactions were more frequent on the active arms (14 High, 7 Low, 6 placebo), as anticipated for a subcutaneously administered antibody and consistent with the expected potential for injection/infusion reactions and immunogenicity. Lupus nephritis flare was reported more frequently on placebo (16) than on the active arms (4 High, 8 Low), consistent with better disease control on OBX-319. No new organ-toxicity signal outside the expected class profile was identified.

12.3 Deaths, serious adverse events, and discontinuations

Serious adverse events were infrequent and distributed across treatment groups without a dose-related pattern (2 High, 1 Low, 1 placebo). There was a single death, in the OBX-319 High-dose arm, attributed to a serious infection consistent with the recognized class risk of B-cell depletion; the case was reviewed by the independent DSMB, and the full narrative is provided in §16.3. Discontinuations were low and broadly comparable across arms (17 High, 13 Low, 10 placebo). No safety signal specific to the active treatment beyond the anticipated class effects was identified.

12.4 Identified risks, laboratory findings, and monitoring

The key identified risks of OBX-319, arising directly from its pharmacology, are serious and opportunistic infections and hypogammaglobulinaemia, and these were the focus of protocol-defined laboratory surveillance and DSMB oversight. Immunoglobulin levels (notably IgG), lymphocyte/B-cell counts, and neutrophils were monitored serially; the profound reduction in circulating CD19+ B cells on the active arms (approximately 210 to approximately 7 cells/µL) reflects the intended pharmacodynamic effect rather than an off-target toxicity. Infection risk was managed through eligibility screening, monitoring, and management guidance. Immunogenicity (binding and neutralizing ADA) was assessed throughout with a tiered validated assay strategy; injection-site and hypersensitivity reactions were monitored per protocol. Routine cardiac safety monitoring showed no signal; a dedicated thorough-QT assessment is not warranted for a monoclonal antibody and was not conducted.

12.5 Safety conclusions

Over the 52-week randomized period, OBX-319 was generally well tolerated, with an adverse-event profile dominated by the expected class effects — infections and injection-site reactions — and infrequent serious events and discontinuations. The safety findings are consistent with the mechanism of profound B-cell depletion and are addressed through defined risk-management and monitoring measures for infection, hypogammaglobulinaemia, injection reactions, and immunogenicity.

13 Discussion and Overall Conclusions

The active arms produced a dose-ordered, statistically significant and clinically meaningful effect at Week 52, with a safety profile consistent with the class. The magnitude of the effect on both the continuous SLEDAI-2K endpoint (LS-mean differences versus placebo of -2.91 and -2.17 for High and Low dose) and the low-disease-activity responder endpoint (52.4% and 33.8% versus 6.0%), together with the concordant pharmacodynamic and serological evidence of target engagement (near-complete CD19+ B-cell depletion, falling anti-dsDNA, and normalising C3/C4), constitutes a coherent and mutually reinforcing efficacy package that supports the selected High-dose regimen while confirming activity at the Low dose. The safety findings — infections, injection-site reactions, and the identified risks of serious/opportunistic infection and hypogammaglobulinaemia, together with expected immunogenicity — are characteristic of B-cell-depleting therapy and are manageable within a defined risk-management and monitoring framework. On balance, the benefit-risk of OBX-319 on a background of standard of care in moderate-to-severe active SLE is favourable over the 52-week induction period. Appendices (16.1 study information, 16.2 patient data listings, 16.3 patient narratives, 16.4 individual data) accompany this report. ICH E3.