Concatenate Last Name, First Name and Middle Name in the textbox.

I would like how to concatenate Last name, First name and Middle in the textbox.
In the textbox I will type :  Doe, Joe H
In the code I put:
see below:
Dim LastName As String = TxtName.Text.Trim() Dim Firstname As String = TxtName.Text.Trim() Dim MiddleName As String = TxtName.Text.Trim() Dim ConnHttp As HttpResponseMessage = client.GetAsync(Convert.ToString((Convert.ToString((Convert.ToString("ABC/api/GetNames?StrNameFam=" & LastName + "&" + "StrFirstName=" & FirstName + "&" + "StrMidName=" & MiddleName).Result How to make a combination of LastName, FirstName MiddleName only in the textbox for searching purposes.
Name:  Scott, Mark K
Thanks