Ustekinumab

Ustekinumab is an anti-IL12/23 IgG1 kappa human monoclonal antibody currently undergoing US Food and Drug Administration review for use as a psoriasis treatment. The candidate has also been evaluated in Phase 2 studies as a treatment for psoriatic arthritis, Crohn disease and multiple sclerosis. In large clinical trials, ustekinumab has proven effective for treating moderate to severe plaque psoriasis. Although long-term follow-up studies are needed to address safety concerns, the hopes are high for psoriasis treatment. Ustekinumab has recently been approved for marketing in Canada and Europe.Key words: ustekinumab, CNTO-1275, Stelara, psoriasis, psoriatic arthritis, Crohn disease, multiple sclerosis     

The Association between Clinical Response to Ustekinumab and Immunogenicity to Ustekinumab and Prior Adalimumab

Background

Immunogenicity due to antidrug antibodies (ADA) to tumor necrosis factor (TNF)-α antagonists is known to decrease treatment response. However, few studies have investigated ADA in ustekinumab, an interleukin-12 and -23 antagonist, in a clinical setting. This study aimed to investigate the immunogenicity of ustekinumab and its clinical consequences in psoriasis.

Methods

This prospective observational study enrolled 76 patients with plaque psoriasis who were treated with ustekinumab for a minimum of 7 months. Blood samples were drawn just prior to scheduled ustekinumab injection during clinic visits. Levels of anti-ustekinumab antibody (AUA) and serum ustekinumab concentration were measured respectively by radioimmunoassays and enzyme-linked immunoassays respectively, and correlated to clinical data and Psoriasis Area and Severity Index (PASI).

Results

AUA was detected in 6.5% of patients after a mean of 13 months of treatment. Patients with positive AUA had significantly lower serum ustekinumab concentrations (0.01 vs. 0.2 mg/L, p<0.001) and lower PASI 50 response than patients without AUA (0% vs. 69%, p = 0.004).The percentage of AUA formation was comparable between patients who had failed previous adalimumab with or without anti-adalimumab antibodies (AAA) (14.3% vs. 12.5%, p = 1.00). However, a higher proportion of switchers without AAA obtaining PASI50 (71.4% vs. 37.5%) and PASI75 response (42.9% vs.12.5%) within 7 months of ustekinumab treatment than with AAA though this difference did not reach statistical significance.

Conclusions

Our results suggest that presence of AUA was significantly associated with treatment failure for ustekinumab, though limited by a small sample size. Also, determining the presence of ADA to antecedent TNF-α antagonists may assist in choosing an optimized subsequent treatment modality achieving treatment success.     

Structural Basis for the Dual Recognition of IL-12 and IL-23 by Ustekinumab

Interleukin (IL)-12 and IL-23 are heterodimeric proinflammatory cytokines that share a common p40 subunit, paired with p35 and p19 subunits, respectively. They represent an attractive class of therapeutic targets for the treatment of psoriasis and other immune-mediated diseases. Ustekinumab is a fully human monoclonal antibody (mAb) that binds specifically to IL-12/IL-23p40 and neutralizes human IL-12 and IL-23 bioactivity. The crystal structure of ustekinumab Fab (antigen binding fragment of mAb), in complex with human IL-12, has been determined by X-ray crystallography at 3.0 Å resolution. Ustekinumab Fab binds the D1 domain of the p40 subunit in a 1:1 ratio in the crystal, consistent with a 2 cytokines:1 mAb stoichiometry, as measured by isothermal titration calorimetry. The structure indicates that ustekinumab binds to the same epitope on p40 in both IL-12 and IL-23 with identical interactions. Mutational analyses confirm that several residues identified in the IL-12/IL-23p40 epitope provide important molecular binding interactions with ustekinumab. The electrostatic complementarity between the mAb antigen binding site and the p40 D1 domain epitope appears to play a key role in antibody/antigen recognition specificity. Interestingly, this structure also reveals significant structural differences in the p35 subunit and p35/p40 interface, compared with the published crystal structure of human IL-12, suggesting unusual and potentially functionally relevant structural flexibility of p35, as well as p40/p35 recognition. Collectively, these data describe unique observations about IL-12p35 and ustekinumab interactions with p40 that account for its dual binding and neutralization of IL-12 and IL-23.     

Ustekinumab Improves Psoriasis without Altering T Cell Cytokine Production,Differentiation, and T Cell Receptor Repertoire Diversity

Ustekinumab is a fully human IgG1κ monoclonal antibody targeting interleukin (IL)-12/23 p40 subunit. The role of IL-12/23-mediated pathway in the mechanism of various inflammatory disorders especially psoriasis has been well recognized. Recently the long-term efficacy and safety of ustekinumab in patients with moderate-to-severe psoriasis has been evaluated in phase 2/3 clinical trials, and the results showed no significant risk for serious adverse effects, infections, or malignancies. Ustekinumab inhibits the function of the IL-12/23 p40 subunit, and therefore it is believed that inhibition of IL-12 p40 pathway decreases IFN-γ production. The major concern for the use of ustekinumab is the possibility of increased immunosuppression due to low IFN-γ production. However, the effects of ustekinumab on CD4⁺ T cell function have not been fully investigated so far. In this study, we explored changes in cytokine production by memory CD4⁺ T cells as well as in the differentiation of naïve T cells to helper T cell (Th) 1, Th2, or Th17 cells in psoriasis patients treated with ustekinumab. The effect of the treatment on T cell receptor repertoire diversity was also evaluated. The results showed that ustekinumab improves clinical manifestation in patients with psoriasis without affecting cytokine production in memory T cells, T cell maturation, or T cell receptor repertoire diversity. Although the number of patients is limited, the present study suggests that T cell immune response remains unaffected in psoriasis patients treated with ustekinumab.