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| 
               
                Title of Each Class of Securities Offered 
               
             | 
             |  |  | 
               
                Amount to be 
                 
            Registered(1)  | 
             |  |  | 
               
                Maximum Offering 
                 
            Price Per Unit  | 
             |  |  | 
               
                Maximum 
                 
            Aggregate Offering Price  | 
             |  |  | 
               
                Amount of 
                 
            Registration Fee(2)  | 
             | ||||||||||||
| 
               
                Common Stock, $0.001 par value per share
               
             | 
             |  |  |  |  | 4,356,059 |  |  |  |  |  | $ | 66.00 |  |  |  |  |  | $ | 287,499,894 |  |  |  |  |  | $ | 31,366.24 |  |  | 
        |  |  |  | 
               
                Per Share 
               
             | 
             |  | 
               
                Total 
               
             | 
             | ||||||
| 
               
                Public offering price 
               
             | 
             |  |  | $ | 66.00 |  |  |  |  | $ | 249,999,948 |  |  | 
| 
               
                Underwriting discount and commissions(1)
               
             | 
             |  |  | $ | 3.96 |  |  |  |  | $ | 14,999,997 |  |  | 
| 
               
                Proceeds, before expenses, to us 
               
             | 
             |  |  | $ | 62.04 |  |  |  |  | $ | 234,999,951 |  |  | 
|  |  |  | 
               
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                As of September 30, 2020 
               
             | 
             | |||||||||||||||
|  |  |  | 
               
                Actual 
               
             | 
             |  | 
               
                Pro Forma 
               
             | 
             |  | 
               
                Pro Forma
                 
            As Adjusted  | 
             | |||||||||
| 
               
                Cash and cash equivalents 
               
             | 
             |  |  | $ | 161,987,083 |  |  |  |  | $ | 56,196,003 |  |  |  |  | $ | 290,695,954 |  |  | 
| Debt: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| 
               
                Convertible note, net of discount of  $3,844,791 
               
             | 
             |  |  | $ | 111,155,209 |  |  |  |  | $ | 111,155,209 |  |  |  |  | $ | 111,155,209 |  |  | 
| 
               
                Long-term debt 
               
             | 
             |  |  |  | — |  |  |  |  |  | 4,682,800 |  |  |  |  |  | 4,682,800 |  |  | 
| 
               
                Total 
               
             | 
             |  |  |  | 111,155,209 |  |  |  |  |  | 115,838,009 |  |  |  |  |  | 115,838,009 |  |  | 
| Stockholders’ equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| 
               
                Preferred stock, $0.001 par value; 2,500,000 shares authorized; none issued and outstanding, actual; 250,000 shares issued and outstanding, pro forma and pro forma as adjusted 
               
             | 
             |  |  |  | — |  |  |  |  |  | 250 |  |  |  |  |  | 250 |  |  | 
| 
               
                Common stock, par value $0.001 per share; 100,000,000 shares authorized; 38,983,824 shares issued and outstanding, actual; 39,659,360 shares issued and outstanding, pro forma; 43,447,238 shares issued and outstanding, pro forma as adjusted 
               
             | 
             |  |  |  | 38,984 |  |  |  |  |  | 39,660 |  |  |  |  |  | 43,447 |  |  | 
| 
               
                Additional paid-in capital 
               
             | 
             |  |  |  | 300,273,819 |  |  |  |  |  | 563,861,731 |  |  |  |  |  | 798,357,894 |  |  | 
| 
               
                Accumulated deficit 
               
             | 
             |  |  |  | (180,483,423) |  |  |  |  |  | (183,854,284) |  |  |  |  |  | (183,854,284) |  |  | 
| 
               
                Accumulated other comprehensive income 
               
             | 
             |  |  |  | 206,626 |  |  |  |  |  | 206,626 |  |  |  |  |  | 206,626 |  |  | 
| 
               
                Total stockholders’ equity
               
             | 
             |  |  | 
                
             | 
            
               120,036,006 
             | 
             |  |  |  | 
                
             | 
            
               380,253,983 
             | 
             |  |  |  | 
                
             | 
            
               614,753,933 
             | 
             |  | 
| 
               
                Total capitalization
               
             | 
             |  |  | $ | 231,191,215 |  |  |  |  | $ | 496,091,992 |  |  |  |  | $ | 730,591,942 |  |  | 
|  | 
               
                Public offering price per share 
               
             | 
             |  |  |  |  |  |  |  |  | $ | 66.00 |  |  | 
|  | 
               
                Historical net tangible book value per share as of September 30, 2020 
               
             | 
             |  |  | $ | 2.67 |  |  |  |  |  |  |  |  | 
|  | 
               
                Pro forma adjustment in historical net tangible book value per share attributable to the pro forma transactions described above 
               
             | 
             |  |  |  | (2.11) |  |  |  |  |  |  |  |  | 
|  | 
               
                Pro forma net tangible book value per share as of September 30, 2020 
               
             | 
             |  |  | $ | 0.56 |  |  |  |  |  |  |  |  | 
|  | 
               
                Increase in net tangible book value per share attributable to this offering 
               
             | 
             |  |  |  | 5.35 |  |  |  |  |  |  |  |  | 
|  | 
               
                Pro forma as adjusted net tangible book value per share after this offering 
               
             | 
             |  |  |  |  |  |  |  |  |  | 5.91 |  |  | 
|  | 
               
                Dilution per share to new investors participating in this offering 
               
             | 
             |  |  |  |  |  |  |  |  | $ | 60.09 |  |  | 
| 
               
                UNDERWRITER 
               
             | 
             |  | 
               
                NUMBER OF SHARES 
               
             | 
             | |||
| 
               
                Morgan Stanley & Co. LLC 
               
             | 
             |  |  |  | 2,272,728 |  |  | 
| 
               
                Jefferies LLC 
               
             | 
             |  |  |  | 505,050 |  |  | 
| 
               
                SVB Leerink LLC 
               
             | 
             |  |  |  | 505,050 |  |  | 
| 
               
                UBS Securities LLC 
               
             | 
             |  |  |  | 505,050 |  |  | 
| 
               
                Total 
               
             | 
             |  |  |  | 3,787,878 |  |  | 
|  |  |  | 
               
                Per Share 
               
             | 
             |  | 
               
                Total 
               
             | 
             | ||||||||||||||||||
|  |  |  | 
               
                Without
                 
            option to purchase additional shares  | 
             |  | 
               
                With
                 
            option to purchase additional shares  | 
             |  | 
               
                Without
                 
            option to purchase additional shares  | 
             |  | 
               
                With
                 
            option to purchase additional shares  | 
             | ||||||||||||
| 
               
                Public offering price 
               
             | 
             |  |  | $ | 66.00 |  |  |  |  | $ | 66.00 |  |  |  |  | $ | 249,999,948.00 |  |  |  |  | $ | 287,499,894.00 |  |  | 
| 
               
                Underwriting discounts and commissions paid by us 
               
             | 
             |  |  | $ | 3.96 |  |  |  |  | $ | 3.96 |  |  |  |  | $ | 14,999,996.88 |  |  |  |  | $ | 17,249,993.64 |  |  | 
| 
               
                Proceeds to us, before expenses 
               
             | 
             |  |  | $ | 62.04 |  |  |  |  | $ | 62.04 |  |  |  |  | $ | 234,999,951.12 |  |  |  |  | $ | 270,249,900.36 |  |  | 
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